Multi-Piece Drill Head and Drill Including the Same

ABSTRACT

One non-limiting aspect of the present disclosure is directed to a multi-piece spade drill head for a spade drill, wherein the spade drill includes an elongate body portion and a cutting portion removably secured to an end of the body portion. The multi-piece spade drill head includes at least two insert pieces, each piece including a cutting edge. The at least two insert pieces are configured to be removably secured to the body portion of the spade drill adjacent one another and with the cutting edges of the insert pieces aligned to together form a cutting edge on an end of the spade drill.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application claiming priorityunder 35 U.S.C. §120 to co-pending U.S. patent application Ser. No.12/368,339, filed Feb. 10, 2009.

BACKGROUND OF THE TECHNOLOGY

1. Field of Technology

The present disclosure relates to cutting tools used in machiningoperations. More particularly, the present disclosure relates toremovable drill heads, and drills including removable drill heads.

2. Description of the Background of the Technology

Drilling is a common metal cutting operation in which material isremoved from a workpiece to provide a bore in or through a workpiece.Drilling is carried out by advancing a rotating drilling tool or “drill”into the workpiece in the direction of the drill's longitudinal axis.Thus, a drill may be defined as a rotating cutting tool used formachining bores in or through a workpiece. Common drill configurationsinclude twist drills and spade drills. A twist drill is characterized byhelical flutes disposed along at least a portion of the length drill andwhich terminate at a working end of the drill (the “drill tip”), whichincludes two cutting edges. A spade drill includes a wide cutting bladeat the drill tip and lacks helical flutes along its length.

With respect to design, there are four main types of drills. A firstdrill type is a single-piece solid drill having either a twist drillconfiguration or a spade drill configuration. Such a drill typicallyincludes cemented carbide material or hard steel and may include acutting tip or “drill head” composed of a very hard material that issoldered or brazed to a steel shank. An example of such a drill isprovided in European Patent Publication No. 0 353 214, which discloses asolid drill particularly useful for percussive drilling and thatcomprises a hard drill head brazed within a slot formed on a tool body.U.S. Pat. No. 6,601,659 discloses a solid twist drill having aspiral-shaped hollow body and a relatively hard cutting tip brazed tothe body. Such a drill provides a lightweight design suited forapplications subjected to substantial torsion and impact, such as occursduring drilling of concrete and brickwork. U.S. Pat. No. 6,655,882discloses a single-piece solid twist drill including an elongate bodyand that is adapted for certain metal working applications. U.S. Pat.No. 7,267,513 discloses a single-piece solid spade drill includingthreads and adapted to increase productivity in certain drillingapplications.

A second drill type is an integrated drilling tool comprising multipleindexable cemented carbide inserts secured by screws or other fastenerson a steel drill body. As is known in the art, an indexable insert maybe removably secured to a holder in two or more cutting orientations,each cutting orientation presenting a different cutting edge. Thus, anindexable insert may be “indexed” to present a different cutting edge tothe workpiece when a cutting edge in use has become unacceptably worn ordamaged. In certain embodiments of this second drill type, severalindexable inserts may be arranged on a single steel body to provide apartially overlapping cutting action and form a complete drill cuttinggeometry. Representative examples are provided in European Patent No. 1280 625, which discloses an integrated drilling tool having twoidentical square-shaped carbide cutting inserts removably mounted on asteel body. U.S. Pat. No. 5,788,431 discloses an integrated drillingtool comprising at least one triangle-shaped carbide cutting insertremovably mounted on a steel body. U.S. Pat. No. 6,527,486 discloses anintegrated drilling tool having multiple generally rectangular-shapedcarbide cutting inserts removably mounted on a steel body.

A third drill type is an integrated drilling tool comprising a singlereplaceable drill head having a twist drill or spade drill configurationmade of either cemented carbide or a hard steel, and wherein the drillhead is mounted on a steel drill body. An example is disclosed in U.S.Pat. No. 4,355,932, which describes an indexable, single-piece spadedrill head mounted on a steel drill body. U.S. Pat. No. 6,044,919 alsodiscloses a single-piece spade drill head mounted on a steel drill body.U.S. Pat. No. 6,224,302 is directed to a single-piece spade drill headhaving a V-shaped end intended to better ensure secure attachment on thedrill's steel tool body. U.S. Pat. No. 7,241,089 discloses asingle-piece spade drill head having an improved geometry includingcurved cutting edges, and wherein the drill head is mounted on a steeldrill body. U.S. Pat. No. 7,306,410 teaches a single-piece twist drillhead that is clamped on a steel drill body. Also, European Patent No. 1280 625 discloses a single-piece twist drill head mounted on a steeltool body and secured in place by two screws.

A fourth drill type is a composite drilling tool comprising twodifferent cemented carbide materials metallurgically bonded together.Examples include a solid drill comprising a relatively harder cementedcarbide material in the drill's core region, and a relativelywear-resistant cemented carbide material in the drill's peripheralregion. U.S. Pat. No. 6,511,265 discloses a composite solid twist drillincluding regions of different cemented carbide materials providingdiffering mechanical properties in the core and surface regions of thedrill. United States Patent Application No. 2007/0042217 discloses asingle-piece spade drill head having a relatively impact resistantcemented carbide grade in a center region, and a relatively wearresistant cemented carbide grade in a peripheral region, and wherein thedifferent cemented carbide materials are metallurgically bondedtogether.

A problem limiting the performance of non-composite drills is that thecutting speed (speed of the cutting edge relative to the workpiece)varies from zero at the drill's center to a maximum cutting speed at thedrill's periphery. Therefore, the conditions promoting wear on a drill'scutting tip can be significantly more aggressive at the periphery thanat the center of the cutting tip. To address this problem, certain knowncomposite drills include different carbide grades, having differentproperties, in the drill's central and peripheral regions. Such anarrangement can be adapted to optimize drilling performance. Themanufacturing costs of composite drills, however, are relatively highbecause manufacturing the drill involves the pressing and sintering ofat least two different cemented carbide materials.

Accordingly, it would be advantageous to provide a drill having aconstruction that improves drilling performance, but which does notrequire the costly steps involved in manufacturing composite drillsincluding multiple (i.e., two or more) regions of cemented carbidematerials.

SUMMARY

According to certain embodiments, a multi-piece spade drill head for aspade drill, the spade drill comprising an elongate body portion and acutting portion removably secured to an end of the body portion, themulti-piece spade drill head may generally comprise at least threeinsert pieces, each piece including a cutting edge, wherein the at leastthree insert pieces are configured to be removably secured to the bodyportion adjacent one another with the cutting edges aligned to togetherform a cutting edge on an end of the spade drill, wherein the alignedcutting edges of adjacent insert pieces form a first interface and asecond interface, and wherein a first distance measured in a directionperpendicular to an axis of rotation of the drill head from the axis ofrotation to the first interface differs from a second distance measuredin a direction perpendicular to the axis of rotation from the axis ofrotation to the second interface.

According to certain embodiments, a multi-piece spade drill head for aspade drill, the spade drill comprising a body portion and a drill headremovably secured to the body portion, the multi-piece spade drill headmay generally comprise a center insert piece forming a central region ofthe spade drill head, the center insert piece including first and secondsides and a cutting edge, a first side insert piece forming at least aportion of a first side region of the spade drill head, the first sideinsert piece comprising a cutting edge and a mating surface configuredto mate with at least a region of the first side of the center insertpiece, and a second side insert piece forming at least a portion of asecond side region of the spade drill head, the second side insert piececomprising a cutting edge and a mating surface configured to mate withat least a region of the second side of the center insert piece, whereinthe center insert piece, the first side insert piece, and the secondside insert piece are configured to be individually removably secured tothe body portion with the mating surface of the first side insert piecemated to the first side of the center insert piece and the matingsurface of the second side insert piece mated to the second side of thecenter insert piece to thereby align the cutting edge of the centerinsert piece with the cutting edge of each of the first side insertpiece and the second side insert piece to together form a cutting edgeon an end of the spade drill, and wherein the aligned cutting edges ofthe center insert piece and first side insert piece form a firstinterface, and the aligned cutting edges of the center insert piece andsecond side insert piece form a second interface, and wherein a firstdistance measured in a direction perpendicular to an axis of rotation ofthe drill head from the axis of rotation to the first interface differsfrom a second distance measured in a direction perpendicular to the axisof rotation from the axis of rotation to the second interface.

According to certain embodiments, a spade drill may generally comprisean elongated body portion including a shank portion at a first end and asecond end configured to removably receive a drill head, and a removablemulti-piece spade drill head comprising at least three insert pieces,each insert piece including a cutting edge and individually removablysecured to the second end of the body portion adjacent one another andwith the cutting edges of the insert pieces aligned to together form acutting edge on the second end of the body portion of the spade drill,wherein the aligned cutting edges of the adjacent insert pieces form afirst interface and the aligned cutting edges of the other adjacentinsert pieces form a second interface, and wherein a first distancemeasured in a direction perpendicular to an axis of rotation of thedrill head from the axis of rotation to the first interface differs froma second distance measured in a direction perpendicular to the axis ofrotation from the axis of rotation to the second interface.

According to certain embodiments, a spade drill may generally comprisean elongated body portion including a shank portion at a first end and asecond end configured to removably receive a drill head, and a removablemulti-piece spade drill head comprising a center insert piece forming acentral region of the spade drill head, the center insert pieceincluding first and second sides and a cutting edge, a first side insertpiece forming at least a portion of a first side region of the spadedrill head, the first side insert piece comprising a cutting edge and amating surface configured to mate with at least a region of the firstside of the center insert piece, and a second side insert piece formingat least a portion of a second side region of the spade drill head, thesecond side insert piece comprising a cutting edge and a mating surfaceconfigured to mate with at least a region of the second side of thecenter insert piece, wherein the center insert piece, the first sideinsert piece, and the second side insert piece are configured to beindividually removably secured to the body portion with the matingsurface of the first side insert piece mated to the first side of thecenter insert piece and the mating surface of the second side insertpiece mated to the second side of the center insert piece to align thecutting edge of the center insert piece with the cutting edge of each ofthe first side insert piece and the second side insert piece to togetherform a cutting edge on an end of the spade drill, wherein the alignedcutting edges of the center insert piece and first side insert pieceform a first interface and the aligned cutting edges of the centerinsert piece and second side insert piece form a second interface, andwherein a first distance measured in a direction perpendicular to anaxis of rotation from the axis of rotation to the first interfacediffers from a second distance measured in a direction perpendicular tothe axis of rotation from the axis of rotation to the second interface.

According to certain embodiments, a multi-piece spade drill head for aspade drill, the spade drill comprising an elongate body portion and acutting portion removably secured to an end of the body portion, themulti-piece spade drill head may generally comprise a center insertpiece comprising a V-shaped cutting edge, and a side insert piececomprising two side regions separated by a recess, each side regionincluding a cutting edge, wherein the center insert piece and the sideinsert piece are configured to be removably secured to the body portionof the spade drill with the center insert piece disposed in the recessof and mating with the side insert piece and so that the cutting edge ofthe center insert piece and the cutting edge of each of the side regionsof the side insert piece are aligned to together form a cutting edge ona terminal portion of the spade drill, wherein the aligned cutting edgesof the center insert piece and first side insert piece form a firstinterface and the aligned cutting edges of the center insert piece andsecond side insert piece form a second interface, and wherein a firstdistance measured in a direction perpendicular to an axis of rotation ofthe drill head from the axis of rotation to the first interface differsfrom a second distance measured in a direction perpendicular to the axisof rotation from the axis of rotation to the second interface.

According to certain embodiments, a spade drill may generally comprisean elongated body portion including a shank portion at a first end and asecond end configured to removably receive a drill head, and a removablemulti-piece spade drill head comprising a center insert piece comprisinga V-shaped cutting edge, and a side insert piece comprising two sideregions separated by a recess, each side region including a cuttingedge, wherein the center insert piece and the side insert piece areconfigured to be removably secured to the body portion of the spadedrill with the center insert piece disposed in the recess of and matingwith the side insert piece and so that the V-shaped cutting edge of thecenter insert piece and the cutting edge of each of the side regions ofthe center insert piece are aligned to together form a cutting edge onthe second end of the spade drill, wherein the aligned cutting edges ofthe center insert piece and one of the two side regions of the sideinsert piece form a first interface and the aligned cutting edges of thecenter insert piece and the other of the two side regions of the sideinsert piece second side insert piece form a second interface, andwherein a first distance measured in a direction perpendicular to anaxis of rotation of the drill head from the axis of rotation to thefirst interface differs from a second distance measured in a directionperpendicular to the axis of rotation from the axis of rotation to thesecond interface.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of certain non-limiting embodiments of theinventions described herein may be better understood by reference to theaccompanying drawings in which:

FIGS. 1( a)-(d) schematically depict various aspects of one non-limitingembodiment of a multi-piece spade drill head constructed according tothe present disclosure;

FIGS. 2( a) and (b) schematically depict various aspects of the centerinsert piece of the multi-piece spade drill head shown in FIGS. 1( a)and 1(b);

FIGS. 3( a)-(c) schematically depict various aspects of the centerinsert piece shown in FIGS. 2( a) and (b), and also show an XYZcoordinate system for defining various geometric aspects of the centerinsert piece;

FIGS. 4( a) and (b) schematically depict various aspects of anon-limiting embodiment of a side insert piece for a multi-piece drillhead according to the present disclosure;

FIGS. 5( a)-(c) schematically depict various aspects of an additionalnon-limiting embodiment of a multi-piece spade drill head according tothe present disclosure;

FIGS. 6( a)-(c) schematically depict various aspects of an additionalnon-limiting embodiment of a multi-piece spade drill head according tothe present disclosure;

FIGS. 7( a) and (b) schematically depict various aspects of anadditional non-limiting embodiment of a multi-piece spade drill headaccording to the present disclosure;

FIGS. 8( a)-(c) schematically depict various aspects of an additionalnon-limiting embodiment of a multi-piece spade drill head according tothe present disclosure;

FIGS. 9( a)-(c) schematically depict various aspects of one non-limitingembodiment of a spade drill assembly according to the presentdisclosure;

FIGS. 10( a)-(c) schematically depict various aspects of an additionalnon-limiting embodiment of a multi-piece spade drill head according tothe present disclosure;

FIGS. 11( a) and (b) schematically depict aspects of an additionalnon-limiting embodiment of a multi-piece spade drill head according tothe present disclosure, wherein the drill head consists of two insertpieces; and

FIGS. 12( a)-(d) are schematic views of an additional non-limitingembodiment of a multi-piece spade drill head according to the presentdisclosure.

FIGS. 13( a) and (b) schematically depict various aspects of the centerinsert piece and a side insert piece for a multi-piece spade drill headaccording to the present disclosure;

FIGS. 14( a)-(c) schematically depict various aspects of onenon-limiting embodiment of a multi-piece spade drill head constructedaccording to the present disclosure; and

FIGS. 15( a) and (b) schematically depict various aspects of onenon-limiting embodiment of a multi-piece spade drill head constructedaccording to the present disclosure.

The reader will appreciate the foregoing details, as well as others,upon considering the following detailed description of certainnon-limiting embodiments of multi-piece (i.e., two or more pieces) drillheads and drill assemblies according to the present disclosure. Thereader also may comprehend certain additional details and advantages ofthe present invention upon carrying out or using the drill heads anddrill assemblies described herein.

DETAILED DESCRIPTION OF CERTAIN NON-LIMITING EMBODIMENTS

In the present description of non-limiting embodiments and in theclaims, other than in the operating examples or where otherwiseindicated, all numbers expressing quantities or characteristics ofingredients and products, processing conditions, and the like are to beunderstood as being modified in all instances by the term “about”.Accordingly, unless indicated to the contrary, any numerical parametersset forth in the following description may be varied depending upon thedesired characteristics one seeks to obtain in the present invention. Atthe very least, and not as an attempt to limit the application of thedoctrine of equivalents to the scope of the claims, any numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as set forth herein supersedes anyconflicting material incorporated herein by reference. Any material, orportion thereof, that is said to be incorporated by reference herein,but which conflicts with existing definitions, statements, or otherdisclosure material set forth herein is only incorporated to the extentthat no conflict arises between that incorporated material and theexisting disclosure material.

The meanings of certain terms used in the present description and claimsare as follows:

As used herein, a “multi-piece” drill head or other article means thatsuch article includes two or more pieces that are associated to form thearticle. It will be apparent form the following description, forexample, that certain embodiments of the multi-piece drill headaccording to the present disclosure may include 2, 3, or more individualinsert pieces that are associated to form the drill head.

As used herein, “mate” or “mated” means that at least a region of eachof the referenced insert pieces are closely abutted together, but arenot physically bonded together. Thus, as used herein, “mated” insertpieces may be individually removed from the drill assembly on which theyare mounted.

As used herein, a “cemented carbide” material refers to a composite of ametal carbide hard phase dispersed throughout a continuous binder phase.The dispersed phase may comprise, for example and without limitation,grains of one or more transition metals selected from titanium,vanadium, chromium, zirconium, hafnium, molybdenum, niobium, tantalumand tungsten. The binder phase that binds or “cements” the metal carbidegrains together may be, for example and without limitation, at least onematerial selected from cobalt, nickel, iron, and alloys of these metals.Additionally, alloying elements such as, for example and withoutlimitation, chromium, molybdenum, ruthenium, boron, tungsten, tantalum,titanium, and niobium may be included in the binder phase to enhancedesired properties. Various cemented carbide materials may be producedby varying at least one of the compositions of the dispersed andcontinuous phases, the grain size of the dispersed phase, the volumefractions of the phases, and the method used to make the compositematerial. Cemented carbides based on a tungsten carbide dispersed hardphase and a cobalt or cobalt alloy binder phase are the mostcommercially important cemented carbide materials available.

Certain non-limiting embodiments of multi-piece drill heads according tothe present disclosure are schematically depicted in the attachedfigures. Three-piece spade drill head 3 is shown in an end view in FIG.1( a) and in a face view in FIG. 1( b). The perspective of FIG. 1( a) isin the direction of arrows A-A in FIG. 1( b). The position of certaingeometric features of drill head 3 that would be hidden in the views ofFIGS. 1( a) and 1(b) are indicated in those figures by dashed lines.Drill head 3 includes three individual insert pieces in the forms ofcenter insert piece 4, side insert piece 5 (to the right of verticalreference line 7 in FIG. 1( b)), and side piece insert 6 (to the left ofline 7). Center insert piece 4 is indexable and can be used in drillhead 3 in the cutting orientation shown in FIG. 1( b), or can be rotated180° about horizontal reference line 9 and used in a second cuttingorientation, wherein a different cutting edge of the center insert piece4 is presented to the workpiece. The indexable nature of center insertpiece 4 is indicated by the indicia “1” and “2” on first face 8, whichidentify the two possible cutting orientations between which centerinsert piece 4 may be indexed.

Center insert piece 4 is 180° rotationally symmetric about a centralaxis that passes longitudinally through the center of fastener hole 10and perpendicular to face 8. Side insert piece 5 and side insert piece 6are identical in design and, as suggested in FIG. 1( a), each sideinsert piece 5,6 includes a first side face having a perimeter largerthan an opposed second side face. The thickness of center insert piece 4and side insert pieces 5 and 6 are identical. When the three insertpieces 4,5,6 are mated in the arrangement shown in FIGS. 1( a) and (b)to form drill head 3, face 8 of center insert piece 4 is substantiallyco-planar with face 11 of side insert piece 5 and with face 12 of sideinsert piece 6. Further, cutting edge 13 on face 8 of center insertpiece 4 is collinear with front cutting edge 14 a on face 11 of sideinsert piece 5, and cutting edge 15 on opposed face 16 of center insertpiece 4 (see FIG. 1( a)) is collinear with front cutting edge 17 on face18 (see FIG. 1( a)) of side insert piece 6.

As shown in FIG. 1( b), side insert piece 5 is generally diamond-shapedwith parallel opposed cutting edges: front cutting edge 14 a is parallelto front cutting edge 14 b, and side cutting edge 14 c is parallel toside cutting edge 14 d. Side insert piece 5 is indexable and, inaddition to the position shown in FIG. 1( b), may be disposed in asecond cutting orientation, in which a different cutting edge iscollinear with a cutting edge of the center insert piece 4 and isoriented to contact a workpiece. Specifically, side insert piece 5 maybe placed in a second cutting orientation by rotating it 180° around aline that is perpendicular to face 11 and passes longitudinally throughthe center of fastener hole 19. In the second cutting orientation, sideinsert piece 5 remains on a side of drill head 3 that is to the right ofreference line 7 as seen in FIG. 1( b). Alternatively, side insert 5 maybe placed in an alternate cutting orientation by rotating it 180° aboutvertical reference line 7 and orienting it within drill head 3 in aposition to the left side of reference line 7 in FIG. 1( b). Sidecutting edge 14 c of side insert piece 5 is oriented slightly tiltedabout point N1 relative to vertical line L1 in FIG. 1( b) to provide asmall relief angle “V” relative to line L1.

Side insert piece 6 has a design identical to side insert piece 5 andmay be indexed between multiple cutting orientation in a correspondingfashion. The distance between point N1 on side insert piece 5 and pointN2 on side insert piece 6 is the drill diameter “DD”, shown in FIG. 1(b), which dictates the diameter of the hole drilled by drill head 3.

Center insert piece 4 of drill head 3 has a unique geometry relative toside insert pieces 5 and 6 and is illustrated schematically in the endview of FIG. 2( a) and the face view of FIG. 2( b). The perspective ofFIG. 2( a) is in the direction of arrows A-A in FIG. 2( b). In order todemonstrate how the center insert piece 4 is designed, FIGS. 2( a) and2(b) include an XYZ coordinate system having an origin at the point “O”located at the center of fastener hole 24, as shown in FIG. 2( b), andat half the thickness “T” of center insert piece 4, as shown in FIG. 2(a). Center insert piece 4 includes first face 22 and opposed second face23, and is 180° rotationally symmetric about the Y axis of coordinatesystem XYZ. With reference to FIG. 2( b), the length “L” of centerinsert piece 4 is defined as the distance “L” between theoretical lines25 and 27 parallel to the X axis. The width “W” of center insert piece4, also shown in FIG. 2( b), is defined as the distance betweentheoretical lines 26 and 28 parallel to the Z axis. As further shown inFIG. 2( b), the center angle “C” of center insert piece 4, shown in FIG.2( b), is defined as the angle between lines extending along cuttingedges 32 and 36 (or extending along cutting edges 38 and 42). The offsetangle “V” of center insert piece 4 is defined as the angle betweentheoretical line 26 and edge 53 (or between any of theoretical line 26and edge 62; theoretical line 28 and edge 56; and theoretical line 28and edge 59).

With reference to FIGS. 2( a) and 2(b), center insert piece 4 is furtherdefined by a series of cutting clearance faces including: cuttingclearance face 31, which extends between cutting edge 32 of first face22 and edge 33 of second face 23; cutting clearance face 34, whichextends between cutting edge 36 of second face 23 and edge 35 of firstface 22; cutting clearance face 37, which extends between cutting edge38 of first face 22 and edge 39 of second face 23; and cutting clearanceface 40, which extends between cutting edge 42 of second face 23 andedge 41 of first face 22.

Again referring to FIGS. 2( a) and 2(b), center insert piece 4 of drillhead 3 is further defined by a series of mating faces configured to matecenter insert piece 4 with side insert pieces 5 and 6 when appropriatelyarranged to form drill head 3. Mating face 51 extends between edge 53 onsecond face 23 and edge 52 on first face 22. Edge 53 is rotated slightlyin a counterclockwise direction (from the perspective of FIG. 2( b))about point “A1” to define an offset angle “V” with theoretical line 26.Similarly, mating face 54 extends between edge 56 on first face 22 andedge 55 on second face 23, and edge 56 is rotated slightly in aclockwise direction (from the perspective of FIG. 2( b)) about point“A2” of theoretical line 28 to define an offset angle relative totheoretical line 28. Mating face 57 extends between edge 59 on secondface 23 and edge 58 on first face 22, and edge 59 is rotated slightly ina counterclockwise direction (from the perspective of FIG. 2( b)) aboutpoint “A3” of theoretical line 28 to define an offset angle relative totheoretical line 28. Similarly, mating face 60 extends between edge 62on the first face 22 and edge 61 on the second face 23, and edge 62 isrotated slightly in a clockwise direction (from the perspective of FIG.2( b)) about point “A4” of theoretical line 26 to define an offset anglerelative to theoretical line 26.

The center insert piece 4 is further defined by two recessed regions,shown in FIG. 2( b). A first recessed region R1 is bounded by straightedge 71 and rounded edges 72. A second recessed region R2 is bounded bystraight edge 73 and rounded edges 74. One of the first and secondrecessed regions R1 and R2 separates the opposing mating faces 51 and 60on one side of center insert piece 4, and the other of R1 and R2separates the opposing mating faces 54 and 57 on another side of thecenter insert piece 4. As illustrated in FIG. 1( b), the first andsecond recessed regions R1 and R2 also provide a relief space betweenthe center insert piece 4 and side inserts pieces 5 and 6 when theinsert pieces are arranged to form three-piece drill head 3.

Center insert piece 4 of drill head 3 provides cutting action as thecentral portion of drill head 3 and also includes complementary matinggeometry with the two side insert pieces 5 and 6 so as to form anintegrated three-piece spade drill head. The geometry of the centerinsert piece 4 can be mathematically defined as a quantitative referencefor the design of the assembled three-piece drill head 3. FIGS. 3(a)-(c) show aspects of center insert piece 4 and an XYZ coordinatesystem for defining the various aspects. In order to mathematicallydefine a planar face like the cutting clearance face 31 shown in theschematic face view of FIG. 3( c), three non-collinear points inthree-dimensional (“3-D”) space are necessary. Such a planar face can bemathematically described as provided in equation (1):

$\begin{matrix}{{f_{CCF}\left( {X,Y,Z} \right)} = {\begin{bmatrix}X & Y & Z & 1 \\x_{1} & y_{1} & z_{1} & 1 \\x_{2} & y_{2} & z_{2} & 1 \\x_{3} & y_{3} & z_{3} & 1\end{bmatrix} = 0}} & {{Eq}.\mspace{14mu} (1)}\end{matrix}$

wherein (x₁, y₁, z₁), (x₂, y₂, z₂), and (x₃, y₃, z₃) represent threenon-collinear points in the XYZ coordinate system through which theplanar face passes. Based on the XYZ coordinate system defined withrespect to FIGS. 2( a) and 2(b), the origin “O” of the XYZ coordinatesystem is set at the center of the fastener hole 24 in the XOZ plane andat a point half way through the thickness of the insert piece 4 in theXOY plane. With reference to FIG. 3( c), three non-collinear points, P₁,P₂, and P₃, can be determined to define the cutting clearance face 31.P₁ (x₁, y₁, z₁) is the theoretical tip point of the center insert piece4 and also the linear extension of the cutting edge 32 on the first face22. P₁ may be defined as follows:

P ₁(x ₁ , y ₁ , z ₁)=(0, T/2, L/2)   Eq. (2)

P₂ (x₂, y₂, z₂) is the intersection point of the theoretical line 26parallel to the Z axis and the linear extension of the front cuttingedge 32 on the top face 22 of the center insert 4. Referring to FIG. 2(b), P₂ (x₂, y₂, z₂) is the same point A1 about which the edge 53 isslightly rotated to provide the offset angle V relative to theoreticalline 26. P₂ may be defined as follows:

P ₂(x ₂ , y ₂ , z ₂)=(W/2, T/2, L/2−(W/2)×tan(Q))   Eq. (3)

wherein “Q” is the angle between cutting edge 31 on first face 22 andtheoretical line 25 (which is parallel to the X axis) and is directlyrelated to the center angle “C”. With reference to the K-K sectionalview in FIG. 3( b) and the side view of FIG. 3( c), the point P₃ (x₃,y₃, z₃) is at edge 33 (shown in dotted lines in FIG. 3( c)) on thesecond face 23 of center insert piece 4 and may be defined as follows:

$\begin{matrix}{{P_{3}\left( {x_{3},y_{3},z_{3}} \right)} = \begin{pmatrix}{{\left\lbrack {{\left( {L/2} \right) \times {\cos (Q)}} - {T \times {\tan (\varphi)}}} \right\rbrack \times {\sin (Q)}},} \\{{{- T}/2},{\left\lbrack {{\left( {L/2} \right) \times {\cos (Q)}} - {T \times {\tan (\varphi)}}} \right\rbrack \times}} \\{\cos (Q)}\end{pmatrix}} & {{Eq}.\mspace{14mu} (4)}\end{matrix}$

wherein φ is the clearance angle of the cutting clearance face 31 of thecenter insert piece 4. Because P₃(x₃, y₃, z₃) is not collinear with P₁(x₁, y₁, z₁) and P₂(x₂, y₂, Z₂), a planar face such as the cuttingclearance face 31 can be exclusively determined. Thus, the cuttingclearance face 31 can be mathematically defined by an expression aspresented in above Eq. (1), which is in the format of a 4×4 matrix.

Because center insert piece 4 is 180° rotationally symmetric about the Yaxis of the XYZ coordinate system in FIGS. 3( a)-(c), a form ofmathematical method known as a geometric transformation can beintroduced to define the remaining cutting clearance faces 34, 37, 40 ofthe center insert piece 4 shown in FIGS. 3( a)-(c). A geometrictransformation involves the mathematical calculation of new coordinatesfor points forming an object from their original positions to theirtransformed positions. A geometric transformation relocates every pointaccording to a specified rule, such as scaling, translation, reflection,or rotation, in a defined coordinate system.

Three non-collinear points (x₁, y₁, z₁), (x₂, y₂, z₂), and (x₃, y₃, z₃)as defined above can be used to establish the cutting clearance face 31of the center insert piece 4 shown in FIGS. 2( a)-(b) and 3(a)-(c). In acoordinate system XYZ as shown in FIGS. 2( a)-(b) and 3(a)-(c), thethree points (x ₁, y₁, z₁), (x₂, y₂, z₂), and (x₃, y₃, z₃) can begrouped into a point matrix format to represent the cutting clearanceface 31, which is designated as “CCF1A”, as follows:

$\begin{matrix}{{{CCF}\; 1A} = \begin{bmatrix}x_{1} & y_{1} & z_{1} & 0 \\x_{2} & y_{2} & z_{2} & 0 \\x_{3} & y_{3} & z_{3} & 0 \\0 & 0 & 0 & 1\end{bmatrix}} & {{Eq}.\mspace{14mu} (5)}\end{matrix}$

A geometric transformation of three points through a rotation of θ=180°about the Y axis in a three-dimensional space can be expressed by thefollowing point matrix:

$\begin{matrix}\begin{matrix}{{R_{Y}\left( {\theta = 180^{{^\circ}}} \right)} = \begin{bmatrix}{\cos (\theta)} & 0 & {- {\sin (\theta)}} & 0 \\0 & 1 & 0 & 0 \\{\sin (\theta)} & 0 & {\cos (\theta)} & 0 \\0 & 0 & 0 & 1\end{bmatrix}} \\{= \begin{bmatrix}{- 1} & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & {- 1} & 0 \\0 & 0 & 0 & 1\end{bmatrix}}\end{matrix} & {{Eq}.\mspace{14mu} (6)}\end{matrix}$

The cutting clearance faces 31 and 37 are 180° rotationally symmetricabout the Y axis, which is actually the indexable relationship betweenthe drill cutting tip “1” (i.e., the portion of center insert piece 4below the X axis as shown in FIGS. 2( b) and 3(c)) and the drill cuttingtip “2” (i.e., the portion of center insert piece 4 above the X axis asshown in FIGS. 2( b) and 3(c)). Thus, the cutting clearance face 37,designated as “CCF2A”, can be defined by the following matrix operation:

$\begin{matrix}\begin{matrix}{{{CCF}\; 2A} = {\left\lbrack {{CCF}\; 1A} \right\rbrack \times \left\lbrack {R_{Y}\left( {\theta = 180^{{^\circ}}} \right)} \right\rbrack}} \\{= \begin{bmatrix}{- x_{1}} & y_{1} & {- z_{1}} & 0 \\{- x_{2}} & y_{2} & {- z_{2}} & 0 \\{- x_{3}} & y_{3} & {- z_{3}} & 0 \\0 & 0 & 0 & 1\end{bmatrix}}\end{matrix} & {{Eq}.\mspace{14mu} (7)}\end{matrix}$

Further, a geometric transformation of three points through a rotationof θ=180° about the Z axis in a three-dimensional space can be expressedby the following point matrix:

$\begin{matrix}\begin{matrix}{{R_{Z}\left( {\theta = 180^{{^\circ}}} \right)} = \begin{bmatrix}{\cos (\theta)} & {\sin (\theta)} & 0 & 0 \\{- {\sin (\theta)}} & {\cos (\theta)} & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}} \\{= \begin{bmatrix}{- 1} & 0 & 0 & 0 \\0 & {- 1} & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}}\end{matrix} & {{Eq}.\mspace{14mu} (8)}\end{matrix}$

The cutting clearance faces 31 and 34 are 180° rotationally symmetricabout the Z axis of the XYZ coordinate system of FIGS. 2( a)-(b) and3(a)-(c). This is because (i) cutting edge 36 on second face 23 must beidentical to cutting edge 32 on first face 22, and (ii) cuttingclearance face 34 must be extended from cutting edge 36 on second face23 to edge 35 on first face 22 as a counterpart to cutting clearanceface 31, which extends from cutting edge 32 on first face 22 to edge 33on second face 23. Thus, these two identical cutting edges 36 and 32 andtwo identical cutting clearance faces 34 and 31 form the basic cuttinggeometry of the center portion of the drill head 3. Therefore, thecutting clearance face 34, designated as “CCF1B” can be defined byfollowing matrix operation:

$\begin{matrix}\begin{matrix}{{{CCF}\; 1B} = {\left\lbrack {{CCF}\; 1A} \right\rbrack \times \left\lbrack {R_{Z}\left( {\theta = 180^{{^\circ}}} \right)} \right\rbrack}} \\{= \begin{bmatrix}{- x_{1}} & {- y_{1}} & z_{1} & 0 \\{- x_{2}} & {- y_{2}} & z_{2} & 0 \\{- x_{3}} & {- y_{3}} & z_{3} & 0 \\0 & 0 & 0 & 1\end{bmatrix}}\end{matrix} & {{Eq}.\mspace{14mu} (9)}\end{matrix}$

Finally, cutting clearance faces 40 and 34 are 180° rotationallysymmetric about the Y axis of the XYZ coordinate system, providing forthe indexable relationship between the drill cutting tip “1” and thedrill cutting tip “2” as shown in FIGS. 2( b) and 3(c). Therefore,cutting clearance face 40, designated as “CCF2B”, can be defined by thefollowing matrix operation:

$\begin{matrix}\begin{matrix}{{{CCF}\; 2B} = {\left\lbrack {{CCF}\; 1B} \right\rbrack \times \left\lbrack {R_{Y}\left( {\theta = 180^{{^\circ}}} \right)} \right\rbrack}} \\{= \begin{bmatrix}x_{1} & {- y_{1}} & {- z_{1}} & 0 \\x_{2} & {- y_{2}} & {- z_{2}} & 0 \\x_{3} & {- y_{3}} & {- z_{3}} & 0 \\0 & 0 & 0 & 1\end{bmatrix}}\end{matrix} & {{Eq}.\mspace{14mu} (10)}\end{matrix}$

The four cutting clearance faces 31, 34, 37, and 40 of center insertpiece 4 have now been defined. Mating faces 51, 54, 57, and 60, shown inFIGS. 2( b) and 3(c), which function as mating faces to properly alignthe two indexable side insert pieces 5 and 6 of the three-piece drillhead 3, also can be defined. Three non-collinear points in 3-D space arenecessary to mathematically define a planar face such as mating face 51.Such a planar face can be mathematically described as follows:

$\begin{matrix}{{f_{CMF}\left( {X,Y,Z} \right)} = {\begin{bmatrix}X & Y & Z & 1 \\x_{4} & y_{4} & z_{4} & 1 \\x_{5} & y_{5} & z_{5} & 1 \\x_{6} & y_{6} & z_{6} & 1\end{bmatrix} = 0}} & {{Eq}.\mspace{14mu} (11)}\end{matrix}$

wherein (x₄, y₄, z₄), (x₅, y₅, z₅), and (x₆, y₆, z₆) represent threenon-collinear points in the XYZ coordinate system of FIGS. 2( a)-(b) and3(a)-(c) through which the planar face passes. With reference to FIG. 3(c), three non-collinear points, P₄, P₅, and P₆, can be determined todefine mating face 51, which comprises edge 52 on first face 22 and edge53 on second face 23. P₄ (x₄, y₄, z₄) and P₅ (x₅, y₅, z₅) are located onopposed ends of edge 52, which is characterized by the length “M” shownin FIG. 3( c) and is slightly tilted counterclockwise about point P4 soas to be oriented at an offset angle “V” relative to theoretical line26. P6 (x6, y6, z6) is on edge 53 (as shown in both FIG. 3( c) and inthe J-J sectional view in FIG. 3( b)) and along the section line J-Jwhich, as shown in FIG. 3( c), is through the midpoint of andperpendicular to edge 52. Points P₄, P₅, and P₆ can be mathematicallyexpressed to define mating face 51 as follows:

P ₄(x ₄ , y ₄ , z ₄)=(W/2−T×tan(φ), T/2,

L/2−(W/2−T×tan(φ))×tan(Q))   Eq. (12)

P ₅(x ₅ , y ₅ , z ₅)=(W/2−T×tan(φ)−M×sin(V), T/2,

L/2−(W/2−T×tan(φ))×tan(Q)−M×cos(V)   Eq. (13)

$\begin{matrix}{{P_{6}\left( {x_{6},y_{6},z_{6}} \right)} = \begin{pmatrix}{{W/2} - {T \times {\tan (\varphi)}} - {{M/2} \times {\sin (V)}} +} \\{{T \times {\tan (\varphi)} \times {\cos (V)}},{{- T}/2},{{L/2} -}} \\{{\left( {{W/2} - {T \times {\tan (\varphi)}}} \right) \times {\tan (Q)}} -} \\{{{M/2} \times {\cos (V)}} - {T \times {\tan (\varphi)} \times {\sin (V)}}}\end{pmatrix}} & {{Eq}.\mspace{14mu} (14)}\end{matrix}$

Therefore, the complementary mating face 51 can be mathematicallydefined by above Equation (11) in the format of a 4×4 matrix. Threenon-collinear points defined by (x₄, y₄, z₄), (x₅, y₅, z₅), and (x₆, y₆,z₆) can be grouped into a point matrix format to represent mating face51, designated as “CMF1A”, as follows:

$\begin{matrix}{{{CMF}\; 1A} = \begin{bmatrix}x_{4} & y_{4} & z_{4} & 0 \\x_{5} & y_{5} & z_{5} & 0 \\x_{6} & y_{6} & z_{6} & 0 \\0 & 0 & 0 & 1\end{bmatrix}} & {{Eq}.\mspace{14mu} (15)}\end{matrix}$

Mating faces 51 and 57 are 180° rotationally symmetric about the Y axisof the XYZ coordinate system of FIGS. 2( a)-(b) and 3(a)-(c) so that thecenter insert piece 4 is fully indexable. The center insert piece 4 maybe indexed between a first cutting orientation in which cutting edges 32and 36 of drill cutting tip region “1” (i.e., the portion of centerinsert piece 4 below the X axis in FIG. 3( c)) are presented to theworkpiece, and a second cutting orientation in which the two cuttingedges of drill cutting tip region “2” (i.e., the portion above the Xaxis) is presented to the workpiece. Thus, mating face 57, designated as“CMF2A”, can be defined in the following expression by following amatrix operation regarding rotational geometric transformation:

$\begin{matrix}\begin{matrix}{{{CMF}\; 2A} = {\left\lbrack {{CCF}\; 1A} \right\rbrack \times \left\lbrack {R_{Y}\left( {\theta = 180^{{^\circ}}} \right)} \right\rbrack}} \\{= \begin{bmatrix}{- x_{4}} & y_{4} & {- z_{4}} & 0 \\{- x_{5}} & y_{5} & {- z_{5}} & 0 \\{- x_{6}} & y_{6} & {- z_{6}} & 0 \\0 & 0 & 0 & 1\end{bmatrix}}\end{matrix} & {{Eq}.\mspace{14mu} (16)}\end{matrix}$

Mating faces 51 and 54 are 180° rotationally symmetric about the Z axisaccording to the XYZ coordinate system shown in FIGS. 3( a) and (c).This is because in the arrangement shown in FIGS. 1( a) and (b), matingface 51 must mate with side insert piece 5 (shown in FIG. 1) and matingface 54 must mate with side insert piece 6 (also shown in FIG. 1).Therefore, mating face 54, designated as “CMF1B”, can be defined by thefollowing matrix operation:

$\begin{matrix}\begin{matrix}{{{CMF}\; 1B} = {\left\lbrack {{CMF}\; 1A} \right\rbrack \times \left\lbrack {R_{Z}\left( {\theta = 180^{{^\circ}}} \right)} \right\rbrack}} \\{= \begin{bmatrix}{- x_{4}} & {- y_{4}} & z_{4} & 0 \\{- x_{5}} & {- y_{5}} & z_{5} & 0 \\{- x_{6}} & {- y_{6}} & z_{6} & 0 \\0 & 0 & 0 & 1\end{bmatrix}}\end{matrix} & {{Eq}.\mspace{14mu} (17)}\end{matrix}$

Further, mating faces 54 and 60 are 180° rotationally symmetric aboutthe Y axis according to the XYZ coordinate system shown in FIGS. 3( a)and (c) so that the center insert piece 4 is fully indexable between afirst cutting orientation in which the cutting edges 32 and 36 of drillcutting tip region “1” (i.e., the portion of center insert piece 4 belowthe X axis in FIG. 3( c)) are presented to the workpiece, and a secondcutting orientation in which the cutting edges of drill cutting tipregion “2” (i.e., the portion above the X axis) are presented to theworkpiece. Therefore, mating face 60, designated as “CMF2B”, can bedefined by following matrix operation:

$\begin{matrix}\begin{matrix}{{{CMF}\; 2B} = {\left\lbrack {{CMF}\; 1B} \right\rbrack \times \left\lbrack {R_{Y}\left( {\theta = 180^{{^\circ}}} \right)} \right\rbrack}} \\{= \begin{bmatrix}x_{4} & {- y_{4}} & {- z_{4}} & 0 \\x_{5} & {- y_{5}} & {- z_{5}} & 0 \\x_{6} & {- y_{6}} & {- z_{6}} & 0 \\0 & 0 & 0 & 1\end{bmatrix}}\end{matrix} & (18)\end{matrix}$

Once Equation (1) and the related geometric transformation matrixesCCF1B, CCF2A, and CCF2B have been established, they can be used as aquantitative reference for the geometric design of all cutting clearancefaces of the indexable center insert piece 4. Also, once Equation (11)and the related geometric transformation matrixes CMF1B, CMF2A, andCMF2B have been established, they can be used as a quantitativereference for the geometric design of all mating faces of the indexablecenter insert piece 4 and the two indexable side insert pieces 5 and 6.

Once center insert piece 4 has been designed based on the aboveequations, the side insert pieces 5 and 6 can be designed accordingly.FIGS. 4( a) and (b) illustrate a simplified side insert piece 80 basedon side insert piece 5 of FIGS. 1( a) and (b). FIG. 4( a) is a sideelevational view of side insert piece 80 showing the positions ofcertain hidden features in dotted lines. FIG. 4( b) is a face viewshowing the positions of certain hidden features in dotted lines. Sideinsert piece 80 includes first face 81, second face 82 (having a smallerperimeter than first face 82), center hole 83, front cutting clearancefaces 84 and 85, and radial cutting clearance faces 86 and 87. Sideinsert piece 80 is 180° rotationally symmetric about center hole 83 andabout the longitudinal axis 88 of center hole 83. Therefore, side insertpiece 80 may be indexed between two cutting orientations. In otherwords, side insert piece 80 includes two pairs of usable cutting edges.A first pair of cutting edges includes cutting edges 90 and 91, and asecond pair of cutting edges includes cutting edge 92 and 93. Radialclearance faces 86 and 87 of side insert piece 80 shown in FIGS. 4(a)-(b) have a complementary geometrical relationship allowing theclearance faces 86, 87 to mate with any of mating faces 51, 54, 57, and60 of center insert piece 4 shown in FIGS. 3( a)-(c).

FIGS. 5( a)-(c) schematically depict an additional non-limitingembodiment of a multi-piece drill head according to the presentdisclosure. FIG. 5( b) is a first face view and FIG. 5( c) is a secondface view of multi-piece spade drill head 99. FIG. 5( a) is an end viewof drill head 99 taken in the direction of arrows A-A shown in FIG. 5(b). The positions of certain features of drill head 99 hidden in theperspectives shown in FIGS. 5( a)-(c) are shown in dotted lines. Centerinsert piece 100 of drill head 99 includes center hole 102 and isindexable between two cutting orientations, as indicated by the regionsof first face 101 identified by numbers “1” and “2”. With reference toFIG. 5( b), center insert piece 100 includes first chip groove 103 andsecond chip groove 104 on first face 101 in positions 180° rotationallysymmetric about center hole 102. With reference to FIG. 5( c), secondface 107 includes chip grooves 105 and 106 in positions 180°rotationally symmetric about center hole 102. With reference to FIG. 5(a), center insert piece 100 also includes web 111 and chisel edge 112.Web 111 is the central region of the drilling geometry at which frontcutting clearance faces 113 and 114 meet. A thicker web provides greaterdrill tip strength for heavy drilling operations, while a thinner webpromotes more efficient cutting and better chip ejection. Chisel edge112 is the intersection of front cutting clearance faces 113 and 114across web 111.

Side insert piece 121 includes: first face 122 (see FIG. 5( b) that issubstantially co-planar with first face 101 of center insert piece 100;second face 123 (see FIG. 5( c)); center hole 124; chip grooves 125 and126 (see FIG. 5( b)) that are 180° rotationally symmetric about centerhole 124; and rounded corners 127 and 128. Side insert piece 131includes: first face 132 that is substantially co-planar with secondface 107 of center insert piece 100; second face 133; center hole 134;chip grooves 135 and 136 that are 180° rotationally symmetric aboutcenter hole 134; and rounded corners 137 and 138. Side insert pieces 121and 131 are identical in design. As suggested in FIG. 5( a), theperimeter of first face 132 is greater than the perimeter of second face133 in side insert piece 131, and the perimeter of first face 122 isgreater than the perimeter of second face 123 in side insert piece 121.

FIGS. 6( a)-(c) schematically depict various aspects of an additionalnon-limiting embodiment of a three-piece drill head according to thepresent disclosure. FIG. 6( a) is an end view schematically depictingthe cutting end of three-piece drill head 150. Drill head 150 includescenter insert piece 151 and side insert pieces 152 and 153. FIG. 6( b)is a schematic first face view of center insert piece 151, along withsectional views of center insert piece 151 taken at lines M-M and N-N inthe direction of the arrows in the first face view. FIG. 6( c)schematically depicts a front face view of a representative side insertpiece of drill head 150, along with a sectional view of the side insertpiece taken at line L-L in the direction of the arrows in the first faceview in FIG. 6( c). Each side insert piece 152 and 153 of drill head 150has a design identical to that shown in FIG. 6( c) and, thus, FIG. 6( c)is representative of the construction of each of side insert pieces 152and 153.

Drill head 150 shown in FIGS. 6( a)-(c) includes double cuttingclearance faces (faces 161 and 162; and 163 and 164) on the centerinsert piece 151 and double clearance faces (171 and 172; and 173 and174) on the front cutting clearances (as defined in FIG. 4( c) for frontcutting clearance faces 84 and 85) of side insert pieces 152 and 153. Asshown in FIG. 6( a) and the Sec. M-M and Sec. N-N views of FIG. 6( b),center insert piece 151 includes paired clearance faces on each of itsfour cutting clearance faces. Specifically, the cutting clearance facesinclude the following pairs of clearance faces: first clearance face 161and second clearance face 162 (shown in Sec. M-M); first clearance face163 and second clearance face 164 (shown in Sec. N-N); first clearanceface 165 and second clearance face 166 (shown in Sec. M-M); and firstclearance face 167 and second clearance face 168 (shown in Sec. N-N).Also, as shown in FIGS. 6( a) and 6(c), each side insert piece 152 and153 includes double clearance faces on each of the front cuttingclearance faces. Specifically, the inserts include the following pairedcutting clearance faces: first clearance face 171 and second clearanceface 172 (as shown on side insert piece 152 in FIG. 6( a)); and firstclearance face 173 and second clearance face 174 (as shown on sideinsert piece 153 in FIG. 6( a)). With respect to the Sec. L-L view ofthe representative schematic side insert piece for drill head 150 shownin FIG. 6( c), first cutting clearance face 175 and second front cuttingclearance face 176 form one pair, and first front cutting clearance face177 and second cutting clearance face 178 (as shown in Sec. L-L view ofFIG. 6( c), form a second pair.

FIGS. 7( a) and 7(b) schematically depict an additional non-limitingembodiment of a three-piece drill head according to the presentdisclosure. Drill head 200 is depicted in an end view in FIG. 7( a) andin a first face view in FIG. 7( b). Each of the center insert piece 201and the side insert pieces 211 and 221 of the drill head 200 isindexable between two cutting orientations in which a different cuttingedge of the particular insert piece is a region of the V-shaped cuttingedge presented to a workpiece on which the drill head would be used.Each of insert pieces 201, 211, and 221 includes chip splitter featureson the cutting clearance face and bumps inside the chip grooves. Centerinsert piece 201 includes a chip splitter structure on each of itscutting clearance faces as follows. As shown in FIG. 7( a) (in theregion identified by indicia “1” in FIG. 7( b)), chip splitter structure202 is provided on cutting clearance face 203, and chip splitter feature204 is provided on cutting clearance face 205. As shown in FIG. 7( a),in the region identified by indexing indicia “2”, chip splitterstructures 206 and 207 are provided. Each of chip splitter structures202, 204, 206, and 207 on center insert piece 200 extends from the firstface 208 through to the second face 209. Side insert piece 211 includesthree chip splitter structures 212 on front cutting clearance face 213and three identical chip splitter structures 214 on front cuttingclearance face 215, such that side insert piece 211 is 180° rotationallysymmetric about center hole 216. All six chip splitter structures 212and 214 on side insert piece 211 extend through the side insert piecefrom first face 217 to second face 218. The positioning and design ofchip splitters structures is the same for side insert pieces 211 and221, and both side insert pieces are 180° rotationally symmetrical abouttheir respective center holes.

Three-piece spade drill head 200 includes multiple bumps in the chipgrooves of the drill head 200 to enhance chip curling and chip breakingduring the drilling process. As shown in FIG. 7( b), in the region ofcenter insert piece 201 designated by number “1”, two bumps 230 areprovided in chip groove 231 on first face 208, and (as indicated bydashed lines) two bumps 232 are provided in chip groove 233 on secondface 209. As also shown in FIG. 7( b), in the region of center insertpiece 201 designated by index number “2”, two bumps 234 are provided inchip groove 235 on first face 208, and (as indicated by dashed lines)two bumps 236 are provided in chip groove 237 on second face 209. Asfurther shown in FIG. 7( b), side insert piece 211 includes four bumps241 on chip groove 242 and four bumps 243 on chip groove 244, and thepositions of the bumps 241 and 243 are 180° rotationally symmetric aboutcenter hole 216. As indicated in FIG. 7( b) by the dotted linesindicating the positions of hidden structures, side insert 221 includesbumps disposed identically to side insert piece 211. Given that thecutting edges of drill head 200 must be oriented to remove material froma workpiece as the drill head rotates, however, the orientation of sideinsert piece 221 is rotated 180° relative to center insert piece 201.

FIGS. 8( a)-(c) and 9(a)-(c) are schematic illustrations illustratingaspects of an additional non-limiting embodiment of a multi-piece spadedrill head and a drill assembly according to the present disclosure.FIG. 8( a) is a schematic end view of the three-piece drill head 240,which includes center insert piece 241 and side insert pieces 242 and243 flanking the center insert piece 241. The center insert piece 241includes a first face 244 and a second face 245. FIG. 8( b) includes aschematic first face view and a side view of the center insert piece 241of the drill head 240. FIG. 8( c) includes a first face view and a sideview of side insert piece 242 of drill head 240. Side insert piece 242includes a radial cutting clearance face (similar to radial cuttingclearance faces 86 and 87 shown in FIG. 4( c)) including first clearancesurface 251 proximate first face 246, and second clearance surface 253proximate second face 247. Side insert piece 243 also includes a radialcutting clearance face including two cutting clearance faces, that is,first clearance surface 252 proximate first face 248 and secondclearance surface 254 proximate second face 249. With reference to FIG.8( a), first radial cutting clearance faces 251 and 252 are curvedsurfaces defining the drilling diameter 255 of the drill head 240,indicated as distance ΦDD. Side insert piece 242 also includes cornerradii 266 and 267, indicated in FIG. 8( c). The designs of side insertpiece 243 and side insert piece 242 are identical.

Mating faces 261, 262, 263, and 264 of center insert piece 241, shown inFIG. 8( b), are complementary to a radial cutting clearance face of theadjacent side insert piece 242 or 243. For example, first radialclearance face 251 and second radial clearance face 253 of side insertpiece 242 are configured to mate with any of mating faces 261, 262, 263,and 264 of center insert piece 241 to allow indexing of the centerinsert piece 241 and the side insert piece 242. The same condition holdstrue with respect to the first and second radial clearance faces 252 and254 of side insert piece 243. It can be seen in FIG. 8 a (an end view)for the center insert 241 that the complementary mating face 261 has afirst clearance face 270 and a second clearance face 271, and thecomplementary mating face 262 has a first clearance face 272 and asecond clearance face 273. It can be seen in FIG. 8( b) (a first faceview and a side view of the center insert piece 241) that complementarymating face 262 includes first clearance face 272 and second clearanceface 273, and complementary mating face 264 includes first clearanceface 274 and second clearance face 275.

FIGS. 9( a)-(c) are schematic illustrations showing aspects of onenon-limiting embodiment of a drilling tool assembly or, more simple, a“drill”, according to the present disclosure. Drill 279 comprisesthree-piece drill head 240 (including insert pieces 241, 242, and 243and as shown in FIGS. 8( a)-(c)) mounted on holder 280. FIG. 9( a) is aschematic plan view of drill 279. FIG. 9( b) is a magnified schematicview of the circled region of drill 279 in FIG. 9( a). FIG. 9( c) is anon-end schematic view of the working end of drill 279, taken in thedirection of arrows C-C in FIG. 9( a) and shown using the scale of FIG.9( b). In each of FIGS. 9( a)-(c) the positions of certain hiddenfeatures of drill 279 are indicated in dotted lines. With reference toFIG. 9( a), holder 280 includes body portion 281 and shank portion 282.As shown in FIGS. 9( b) and 9(c), center insert piece 241 and sideinsert pieces 242 and 243 are secured on a terminal end of body portion281 by screws 283, 284, and 285, respectively. Body portion 281 includestwo chip flutes 286 and two cooling holes 287. Shank portion 282 of bodyportion 281 of tool holder 280 is adapted so that drill 279 may beattached to a drilling or milling machine.

Insert pieces 241, 242, and 243 may be detached from holder 280 byremoving screws 283, 284, and 285, respectively, and may be indexedbetween alternate cutting orientations, as discussed above. Also, itwill be understood that insert pieces 241, 242, and 243 are mated andare not connected together, but rather are separately secured to holder280 by their respective screws and are individually removable. Themating relationship between side insert pieces 242, 243 and the centerinsert piece 241, as discussed above, presents a substantially seamless,generally V-shaped cutting edge to the workpiece, despite the fact thatthe drill head 240 has a multi-piece construction. The multi-piececonstruction allows for many unique advantages. For example, centerinsert piece 241 may be separately indexed between alternate cuttingorientations. Also, side insert pieces 242 and 243 may be detached,rotated, and their positions exchanged to index their respective cuttingedges between alternate cutting orientations, and without the need toalso index center insert piece 241. To address wear and/or damage, anyof insert pieces 241, 242, and 243 may be individually indexed orreplaced, without the need to also index or replace the remaining insertpiece(s).

Also, the materials from which the center insert piece 241 and the sideinsert pieces 242 and 243 are made can differ. Given that the cuttingspeed of side insert pieces 242 and 243 exceeds that of the centerinsert piece 241, the forces promoting wear experienced by the insertpieces 242 and 243 will likely exceed those experienced by center insertpiece 241. Given the multi-piece (i.e., two or more pieces) constructionof drill heads according to the present disclosure, drill head 240, forexample, may include side insert pieces 242 and 243 made of a materialhaving greater wear resistance than center insert piece 241, therebypromoting more even wear of drill head 240 across the length of thegenerally V-shaped cutting edge presented to the workpiece. Even if theindividual insert pieces of drill head 240 are composed of likematerials and side insert pieces 242 and 243 wear at a rate greater thancenter insert piece 241, side insert pieces 242 and 243 may be indexedor replaced separately from center insert piece 241. This feature avoidsthe necessity to replace the entire drill head 240 when only regions ofthe drill head experience unacceptable wear and/or damage.

FIGS. 10( a)-(c) are schematic views showing aspects of an additionalnon-limiting embodiment of a multi-piece spade drill head according tothe present disclosure. Three-piece spade drill head 300 is shownassembled and in a schematic end view in FIG. 10( a) and includes centerinsert piece 301 and side insert pieces 302 and 303 flanking centerinsert piece 301. FIG. 10( b) schematically depicts center insert piece301 in both a first face view (left side of the figure) and a side view(right side of the figure) taken in the direction of arrows B-B adjacentthe first face view. In the first face view of FIG. 10( b) the positionsof certain hidden features of drill head 300 are indicated in dottedlines. The design of side insert piece 303 is identical to that of sideinsert piece 302.

Center insert piece 301 does not include a central fastener hole asincluded in the embodiments discussed above. Instead, as shown in FIG.10( b), center insert piece 301 includes slot 304 on first face 305 anda set screw or clamp (not shown) attached to the holder may be used tosecure the center insert piece 301 into an insert pocket of the holder.Utilizing a center insert piece 301 without a fastener hole isparticularly useful in the design of small size multi-piece spade drillsaccording to the present disclosure. Each of the insert pieces 301, 302,and 303 includes two pairs of cutting edges to provide indexingcapability of each insert piece between two cutting orientations. Asshown in FIG. 10( b), center insert piece 301 includes a first set ofcutting edges 306 and a second set of cutting edges 307. As shown inFIG. 10( c), side insert piece 302 (which is identical to side insertpiece 303) includes a first set of cutting edges 308 and a second set ofcutting edges 309. The drilling diameter 310 of drill head 300,indicated as ΦDD in FIG. 10( a), is formed by a radial cutting clearanceface of side insert piece 302 including a curved face 311, and a radialcutting clearance face of side insert piece 303 including a curved face312. Each of mating faces 321, 322, 323, and 324 of center insert piece301, shown in FIG. 10( b), comprises a curved face and a planar face.For example, as shown in the side view of center insert piece 301 inFIG. 10( b), mating face 322 includes curved face 325 and planar face326, which are complementary in shape to each radial cutting clearanceface of the side insert pieces 302 and 303, which each also comprise acurved face and a planar face. For example, curved face 325 and planarface 326 are complementary in shape and may mate with curved clearanceface 311 and planar face 327 of side insert piece 302 (see FIG. 10( c)).

FIGS. 11( a) and (b) are schematic views of an additional non-limitingembodiment of a multi-piece spade drill head according to the presentdisclosure, wherein the drill head includes two insert pieces that mateto together form a generally V-shaped cutting edge of the desireddiameter. Two-piece drill head 251 includes center insert piece 252 anda single, generally U-shaped side insert piece 253 mating simultaneouslywith opposed sides of center insert piece 252. In order to clarify themating relation between the center insert piece 252 and the side insertpiece 253, the top view in FIG. 11( a) showing an end view of theassembled drill head 251 is broken into two separate end views, oneshowing the center insert piece 252 in isolation and one showing theside insert piece 253 in isolation. FIG. 11( a) includes: an end view ofthe assembled drill head 251 (top view) showing the end that would bepresented to the workpiece; an end view in isolation of the drill head'scenter insert piece 252 (middle view); and an end view of in isolationof side insert piece 253 (bottom view) that is taken in the samedirection as in the top view in FIG. 11( a). FIG. 11( b) includes afirst face view of assembled drill head 251 and two sectioned viewstaken at P-P and R-R in the direction of the arrows. The first face 254of center insert piece 252 is aligned so as to be substantially coplanarwith the top face 256 of side insert piece 253, and the second face 255of the center insert piece 252 is aligned so as to be substantiallycoplanar with the bottom face 257 of the side insert piece 253. Thecenter insert piece 252 includes two mating faces 261 and 262 in theregion of center insert piece 252 identified by indicia “1”. The centerinsert piece also includes two mating faces 263 and 264 in the region ofthe center insert piece 251 identified by indicia “2” (see middle viewof FIG. 11( a) and FIG. 11( b)). Mating faces 261 and 262 of centerinsert piece 252 are shown in the top view of FIG. 11( a) and in FIG.11( b) mated with complementary mating faces 265 and 266, respectively,of side insert piece 253.

In the particular embodiment depicted in FIGS. 11( a) and (b), onlycenter piece insert 252 of drill head 251 is indexable between twocutting orientations. Center insert piece 252 may be indexed from thecutting orientation shown in FIG. 11( b) to a second cutting orientationby rotating center insert piece 252 180° about fastener hole 267 so thatthe region identified by indicia “2” is oriented toward the workpieceand mating faces 263 and 264 of center insert piece 252 mate withcomplementary mating faces 265 and 266, respectively, of side insertpiece 253.

To form a generally V-shape cutting of the desired cutting diameter,cutting edge 271 of first face 254 of center insert piece 252 is alignedwith cutting edge 273 of face 256 of side insert piece 253, and cuttingedge 272 of second face 255 of center insert piece 252 is aligned withthe cutting edge 274 of face 257 of side insert piece 253. Center insertpiece 252 also includes chip grooves 281 and 282 on face 254 and chipgrooves 283 and 284 (positions indicated by dashed lines in FIG. 11( b))on face 255. Side insert piece 253 includes chip groove 285 on face 256and chip groove 286 (position indicated by dashed line in FIG. 11( b) onface 257. As illustrated in the bottom view of FIG. 11( a), side insertpiece 253 includes vertical face 291 proximate face 257 and verticalface 292 proximate face 256. As shown in the Sec. P-P and R-R views ofFIG. 11( b), center insert piece 252 leans against vertical faces 291and 292, which helps to securely interconnect the two insert pieces whenthe insert pieces are mounted on the drill body of a drill. Centerinsert piece 252 is secured to a drill body by a screw (not shown)passing through fastener hole 267, and side insert piece 253 is securedto a drill body by two screws (not shown) passing through fastener holes293 and 294. The side insert piece 253 also comprises a slot 295 usedfor locating the side insert piece 253 on a drill body and a slot 296 toprovide some relief room for a drill tip portion (by indicia “1” or “2”)of the center insert piece 252.

Although the multi-piece drill head embodiment 251 includes only twoinsert pieces and, therefore, does not provide certain advantages ofother embodiments described herein including more than two insertpieces, drill head 251 may be constructed so that center piece insert252 and side insert piece 253 are made of different cemented carbide,hard steel, or other materials. In that way, for example, the differentwear conditions at the center and edges of the drill head may beaddressed.

Alternate arrangements for aligning the components of a multi-piecedrill heads according to the present disclosure are contemplated. FIGS.12( a)-(d) are schematic views showing aspects of an additionalnon-limiting embodiment of a multi-piece spade drill head according tothe present disclosure. Three-piece spade drill head 400 is shown in aschematic end view in FIG. 12( a) and in a first face view in FIG. 12(b). Drill head 400 includes center insert piece 401 and side insertpieces 402 and 403 flanking center insert piece 401. FIG. 12( c)schematically depicts center insert piece 401 in both a first face view(right side of the figure) and a side view (left side of the figure)taken in the direction of arrows B-B adjacent the first face view. FIG.12( d) schematically depicts side insert piece 402 in both a first faceview (left side of the figure) and a side view (right side of thefigure) taken in the direction of arrows C-C adjacent the first faceview. The design of side insert piece 403 is identical to that of sideinsert piece 402.

Center insert piece 401 includes four vertical planar mating surfaces411, 412, 413, and 414, all of which are substantially perpendicular tofirst face 410. Side insert piece 402 includes correspondingcomplementary surfaces 415 and 416, and side insert piece 403 includescorresponding complementary surfaces 417 and 418. Referring to sideinsert piece 402 shown in FIG. 12( d), a recessed portion 421 created byremoving the region enclosed by dashed lines from side insert piece 402provides complementary surface 415 at one corner of side insert piece402. Similarly, a recessed portion 423 created by removing the regionenclosed by dashes lines from side insert piece 402 providescomplementary surface 416 at a second corner of side insert piece 402.Complementary surfaces 415 and 416 are substantially perpendicular toface 422 and are 180° rotationally symmetric about center hole 425.Thus, as shown in FIG. 12( d), a relatively geometrically simple matingsurface, such as mating surface 416, is separated in a radial directionfrom a relatively geometrically complex cutting face, such as cuttingface 426. In the arrangement shown in FIGS. 12( a)-(c), mating surface411 of center insert piece 401 is mated with complementary surface 415of side insert piece 402, and mating surface 412 of center insert piece401 is mated with complementary surface 417 of side insert piece 403.

Certain significant advantages provided by the multi-piece constructionof drill heads and drills described herein are discussed above. Asignificant advantage of the multi-piece construction is that variousregions of the drill head may be embodied in separately removable insertpieces. Thus, regions of the drill head that experience forces moreaggressively promoting wear and/or breakage may be selectively replacedor indexed to present a new cutting edge to the workpiece. Given thatthe cutting speed of outer regions of the cutting edge (regions remotefrom the rotational axis of the drill) is greater than the cutting speednearer the drill's rotational axis, the outer regions of a drill headtypically are subjected to significantly greater wear if the drill headis made of a homogenous material. Once the outer regions of the cuttingedge of, for example, a conventional spade drill head have worn orbecome damaged to an unacceptable degree, the entire drill head (if itis removable) or the entire drill (if the drill head is fixed) must bereplaced. In a drill head having the unique multi-piece constructionaccording to the present disclosure, the cutting edge is formed bymultiple (i.e., two or more) separately removable insert pieces. Thus,only those insert pieces having cutting edges that suffer fromunacceptable wear and/or breakage during use need to be indexed orreplaced.

Also, the multi-piece construction described herein allows for thepossibility that different insert pieces of a multi-piece drill headaccording to the present disclosure are made from different materials.For example, with respect to three-piece drill head 240 illustrated inFIGS. 9( a)-(c), side insert pieces 242 and 243 may be made from acemented carbide or other suitable material having improved wearresistance relative to a cemented carbide or other suitable materialfrom which the center insert piece 241 is made. Also, for example, withrespect to two-piece drill head 251 illustrated in FIGS. 11( a)-(b),side insert piece 253 is made from a cemented carbide or other suitablematerial having improved wear resistance relative the material fromwhich the center insert piece 252 is made. In this way, the greatercutting speeds experienced at the outer regions of the cutting edge maybe addressed by enhancing the wear resistance properties in thoseregions. Also, the ability provided by a multi-piece drill head designto enhance the wear resistance of regions of the drill head subjected tomore extreme wear conditions can be used to even the rate of wearexperienced along the entire cutting edge. Once the degree of wear alongthe cutting edge becomes unacceptable, the entire drill head may bereplaced (by installing new insert pieces on the drill) or theindividual inserts may be indexed to an alternate cutting orientation.

As noted in the Background section above, certain one-piece drillembodiments are known wherein different metallurgically bonded regionsof the drill are composed of different composite materials. In this way,the tendency for outer regions, which run at faster cutting speeds, towear at a faster rate can be addressed by providing composite materialshaving greater wear resistance in those outer regions. As further noteabove, however, the production of composite drills requires additionalprocessing steps and expense. The present multi-piece construction canbe adapted to provide drill heads having enhanced wear resistanceproperties in the regions where needed, without the need to produce thedrill head as a one-piece, monolithic component. Each of the two or moreindividually removable insert pieces making up a drill head according tothe present disclosure may be made of a single material such as, asingle cemented carbide, tool steel, or other suitable material, havingmechanical properties (for example, wear resistance, toughness, andstrength) desired for the particular region of the drill head.

Imperfect machining of one or more of the insert pieces may impact onthe performance of certain embodiments of multi-piece drill headsaccording to the present disclosure. For example, imperfect machining ofthe center insert piece and/or one or more side insert pieces mayprevent a cutting edge of the center insert piece from precisely meetinga cutting edge of a side insert piece. As a result, a gap may existbetween a cutting edge of a center insert piece and a cutting edge of aside insert piece. Again referring to FIG. 1( c), a multi-piece drillhead 3 may comprise a center insert piece 4, a first side insert piece5, and a second side insert piece 6. The mating relationship between thecenter insert piece 4 and side insert pieces 5,6, as shown in FIG. 1(d), preferably presents a seamless (i.e., gap-less), generally V-shapedcutting edge to the workpiece. A seamless multi-piece drill head mayhave cutting edges 13, 15 of center insert piece 4 that are one ofgenerally aligned, mostly aligned, and substantially aligned, but notaligned, with the cutting edges 14 a, 17 of side insert pieces 5, 6,respectively. As generally used herein, the terms “generally aligned”,“mostly aligned”, and “substantially aligned” refer to varying degreesof non-collinear arrangement of two or more objects. Referring to FIG.1( c), the cutting edge 13 of center insert piece 4 may not be alignedwith the front cutting edge 14 a of side insert piece 5, and/or thecutting edge 15 of center insert piece 4 may not be aligned with thefront cutting edge 17 of side insert piece 6. Referring to FIG. 1( a),in contrast, the cutting edges 13, 15 of center insert piece 4 arealigned with the cutting edges 14 a, 17 of side insert pieces 5, 6,respectively, to form a substantially seamless V-shaped cutting edge onthe multi-piece drill head.

The mating relationship between the center insert piece 4 and the sideinsert pieces 5, 6 may contribute to the alignment of the cutting edgesof the insert pieces. Generally, the center insert piece 4 of the drillhead includes complementary mating geometry with the abutting sideinsert pieces to together form an integrated multi-piece spade drillhead having aligned cutting edges. The center insert piece 4 of thedrill head, however, may include non-complementary mating geometry withthe side insert pieces resulting from, for example, imperfect machiningof at least one of the insert pieces. For example, the mating facesand/or recess regions of the center insert piece 4 may not preciselymeet with the side insert pieces 5, 6. The imperfect mating of thecenter insert piece 4 and side insert pieces 5, 6 may cause imperfectalignment between the cutting edges 13, 15 of center insert piece 4 andthe cutting edges 14 a, 17 of side insert pieces 5, 6, respectively.

The alignment of the cutting edges of the insert pieces may becharacterized by the presence, if any, of gaps between the cutting edgesof the insert pieces. Referring to FIG. 1( a), for example, two alignedcutting edges may not form a gap. Referring to FIG. 1( c), in contrast,two generally aligned cutting edges may form a gap. The imperfectalignment of the cutting edges 13, 15 of the center insert piece 4 tothe cutting edges 14 a, 17 of the side insert pieces 5, 6 may contributeto the formation of at least one gap 5 a, 6 a at the interface of thecenter insert piece 4 and side insert pieces 5, 6 along the V-shapedcutting edge of the drill head.

Imperfect alignment of the cutting edges of a multi-piece drill headaccording to the present disclosure may contribute to undesirableeffects during the drilling process. For example, two generally alignedcutting edges may leave residual material in the bore formed inworkpiece by the drill head. As shown in FIGS. 1( c) and (d), gaps 5 aand 6 a along the cutting edge of drill head 3, for example, maycontribute to residual material R left within the bore H drilled in aworkpiece. As shown in FIG. 1( c), in the drill head 3, the lateraldistance EE from an axis of rotation 7 of the drill head 3 to theinterface of the center insert piece 4 and side insert piece 6 is equalto the lateral distance FF from the axis of rotation 7 of the drill head3 to the interface of the center insert piece 4 and the side insertpiece 5. (The lateral distances EE and FF are measured in a directionperpendicular to an axis of rotation of the drill head 3.) The imperfectmating of the center insert piece 4 and side insert piece 5 may cause agap 5 a to form at the interface of the center insert piece 4 and sideinsert piece 5 at the cutting edge. The imperfect mating of the centerinsert piece 4 and side insert piece 6 may cause a gap 6 a to form atthe interface of the center insert piece 4 and side insert piece 6 atthe cutting edge. Because the gaps 5 a, 6 a are equidistant from therotational axis 7 of the drill head and sweep through the same circularpath during drilling, as indicated in FIG. 1( d), a ring-shaped ridge ofresidual workpiece material R may remain within the drill bore H oncompletion of the drilling process. Also, because a region of thecutting edge geometry is absent at equidistant gaps 5 a and 6 a and doesnot sweep through the workpiece as the drill head 3 rotates, the drillhead 3 may wear relatively quickly in the gap regions as material isremoved from the workpiece. The present inventors perceived that itwould be beneficial to provide an alternative multi-piece drill headdesign that avoids the possibility of equidistant gaps in the V-shapedcutting edge of a multi-piece drill head according to the presentdisclosure.

According to certain alternate embodiments, a multi-piece spade drillhead may be configured to reduce or eliminate the undesired effectscaused by imperfect mating of the insert pieces and/or imperfectalignment of the cutting edges during the drilling process. In suchalternate embodiments, a multi-piece spade drill head for a spade drillcomprises at least three insert pieces, each piece including a cuttingedge, wherein the at least three insert pieces are configured to beremovably secured to a body portion adjacent one another, with thecutting edges of the insert pieces aligned to together form a generallyV-shaped cutting edge on an end of the spade drill. Aligned cuttingedges of a first pairing of adjacent insert pieces form a firstinterface, aligned cutting edges of a second pairing of adjacent insertpieces form a second interface, and a first distance measured from anaxis of rotation of the drill head to the first interface differs from asecond distance measured from the axis of rotation of the drill head tothe second interface. The multi-piece spade drill head may comprise acenter insert piece and first and second side insert pieces flankingopposite sides of the center insert piece. The aligned cutting edges ofthe center insert piece and the first side insert piece abut or approachat a first interface, and the aligned cutting edges of the center insertpiece and the second side insert piece abut or approach at a secondinterface, wherein a first distance measured from an axis of rotation ofthe drill head to the first interface differs from a second distancemeasured from the axis of rotation of the drill head to the secondinterface.

As shown in FIG. 13( a), the center insert piece 501 may comprise twogenerally V-shaped cutting edges formed by cutting edge 511 and cuttingedge 512. Each of the cutting edges 511, 512 may comprise a longercutting edge portion and a shorter cutting edge portion. Cutting edge511 may comprise a longer cutting edge portion 511 a and a shortercutting edge portion 511 b. Cutting edge 512 may comprise a longercutting edge portion 512 a and a shorter cutting edge portion 512 b. Thelength of longer cutting edge portion 511 a and the length of longercutting edge portion 512 a may be the same. The length of shortercutting edge portion 511 b and the length of shorter cutting edgeportion 512 b may be the same. Accordingly, the apex of each V-shapedcutting edge 511, 512, which is positioned along the axis of rotation ofthe drill head, may bifurcate the cutting edges 511, 512 of the centerinsert piece 501 into two unequal lengths due to the longer cutting edgeportions 511 a, 512 a and the shorter cutting edge portions 511 b, 512b.

With further reference to FIG. 13( a), the center insert piece 501 maycomprise two recessed regions. The first recessed region may be bound bya straight edge 571 and side edges 572 a, 572 b. The second recessedregion may be bound by a straight edge 573 and side edges 574 a, 574 b.The length of each of the straight edges 571, 573 may be the same. Thelength of the two side edges forming each recessed region of centerinsert piece 501 may be unequal to accommodate the unequal length of thelonger and shorter cutting edge portions forming each of cutting edges511, 512. For example, the length of side edge 572 a may be differentthan the length of side edge 572 b, and the length of side edge 574 amay be different than the length of side edge 574 b. Also, the length ofeach of the side edges of the first recessed region may the same as thelength of a side edge of the second recessed region. For example, thelength of side edge 572 a may be the same as the length of side edge 574b, and the length of side edge 572 b may be the same as the length ofside edge 574 a.

The center insert piece 501 is indexable. As such, the center insertpiece 501 can be used in a drill head in the orientation shown in FIG.13( a), wherein cutting edge 512 is presented to a workpiece, or can berotated 180° about the center 515 of fastener hole 519 and used in asecond cutting orientation, cutting edge 511 is presented to theworkpiece. The indexable nature of center insert piece 501 is indicatedby the indicia “1” and “2” on the face of piece 501, which identify thetwo possible cutting orientations between which the center insert piece501 may be indexed.

As shown in FIG. 13( b), side insert piece 502 is generallydiamond-shaped and includes parallel opposed cutting edges. Side insertpiece 502 may comprise a first cutting edge comprising a front cuttingedge 521 and a side cutting edge 523, and a second cutting edgecomprising a front cutting edge 522 and a side cutting edge 524. Frontcutting edge 521 is parallel to front cutting edge 522, and side cuttingedge 523 is parallel to side cutting edge 524. The length of the sidecutting edges 523, 524 may be the same. The length of the first frontcutting edge 521 may be shorter than the length of the second frontcutting edge 522. As discussed below, the difference in the lengths offirst and second cutting edges 521, 522 accommodates the difference inthe lengths of the longer and shorter cutting edge portions formingcutting edges 511, 512 when side insert pieces 502 are mated to opposedsides of a center insert piece 501 to form an embodiment of amulti-piece drill head according to the present disclosure.

Side insert piece 502 is indexable and, in addition to the first cuttingorientation shown in FIG. 13( b), in which cutting edges 522, 524 arepresented to a workpiece, may be disposed in a second cuttingorientation in which a different cutting edge is oriented to contact theworkpiece. Specifically, side insert piece 502 may be placed in a secondcutting orientation by rotating it 180° around a line that isperpendicular to the face and passes longitudinally through the center525 of fastener hole 529.

As shown in FIGS. 13( a) and (b), at least one of the three insertpieces may include one or more indicia to facilitate alignment a centerinsert piece 501 and two side insert pieces 502 to form the multi-piecedrill head. For example, the center insert piece 501 may comprise atleast one arrow-shaped indicator 516 on the top face of the centerinsert piece 501. The side insert piece 502 may comprise an arrow-shapedindicator 526 on first face of the side insert piece to indicate properorientation of the insert piece 502, wherein the arrow is directedtoward the cutting edge of the adjacent, abutting insert piece. Asimilar arrow-shaped indicator may also be provided on the second,opposite face of the insert piece 502 to identify proper orientation.Although FIGS. 13( a) and (b) show arrow-shaped indicia, it will beunderstood that the indicia may comprise any symbol that aids incorrectly orienting and aligning the insert pieces to form a multi-piecedrill head according to the present disclosure.

FIGS. 14( a)-(c) illustrate a multi-piece drill head comprising a centerinsert piece 501 having cutting edges 512 a and 512 b of unequal length,and two side insert pieces 502, 503, each comprising a front cuttingedge 522, 533 and a side cutting edge 524, 534, respectively. Thealigned cutting edges 533, 512 a, 512 b, 522 form a generally V-shapedcutting edge. The two side insert pieces 502, 503 may be identical. Thecutting edge 512 of the center insert piece 502 may comprise a longercutting edge portion 512 a and a shorter cutting edge portion 512 b.Each of the two side insert pieces 502, 503 may comprise a longercutting edge portion and a shorter cutting edge portion. For example,side insert piece 502 may comprise a longer front cutting edge 522 andan oppositely disposed shorter cutting edge (not numbered). The secondside piece 503 also may comprise a shorter front cutting edge 533 and anoppositely disposed longer cutting edge (not numbered).

As illustrated in FIG. 14( a), the longer cutting edge portion 512 a ofthe center insert piece 501 may be aligned with the shorter frontcutting edge 533 of the side insert piece 503 at a first interface. Asshown in FIG. 14( b), which is front-end view of drill head arrangementshown in FIG. 14( a), the first interface may comprise aligning face 541on center piece 501 and aligning face 542 of side insert piece 503. Thefirst interface may comprise the longer cutting edge portion 512 a ofthe center insert piece 501 and the shorter cutting edge portion 533 ofside insert piece 503. The shorter cutting edge portion 512 b of thecenter insert piece 501 may be aligned with the longer front cuttingedge 522 of the side insert piece 502 to form a second interface. Asshown in FIG. 14( b), the second interface may comprise aligning face543 on the center piece 510 and aligning face 544 of the side insertpiece 502. The second interface may comprise the shorter cutting edgeportion 512 b of the center insert piece 501 and the longer cutting edgeportion 522 of side insert piece 502.

With reference to FIGS. 14( a) and (b), the lateral distance AA measuredfrom the rotational axis 545 of the drill head (which includes the apexof the V-shaped cutting edge) to the first interface (measured in adirection perpendicular to axis 545) differs from the lateral distanceBB measured from the rotational axis 545 to the second interface (alsomeasured in a direction perpendicular to axis 545). The difference inlateral distances AA and BB may reduce or eliminate residual materialremaining within the bore during the drilling process in the event thatthere is imperfect mating of the insert pieces and/or imperfectalignment of the cutting edges. For example, because of the differentlateral distances AA and BB to the interfaces, any gap in the cuttingedge that exists at a first interface will not sweep a circular paththat is aligned with any gap that may exist at the second interface. Assuch, any workpiece material that is not machined from the workpiece bya cutting edge region at a first interface (because a gap exists at thefirst interface) will be removed by a cutting edge region equidistantfrom the rotational axis at the opposite side of the drill head. Inother words, material that is not machined from a workpiece because agap exists at the first interface due to imperfect mating of the insertpieces 501, 502 and/or imperfect alignment of the cutting edges 512 b,522 will be machined from the workpiece by the opposed cutting edgeregion of the drill head, e.g., cutting edge 512 a, because the lateraldistance BB′, which is equal to BB, is shorter than AA. Similarly,material that is not machined from a workpiece because a gap exists atthe second interface resulting from imperfect mating of the insertpieces 501, 503 and/or imperfect alignment of the cutting edges 512 a,533 will be machined from the workpiece by the opposed cutting edgeregion of the drill head, e.g., cutting edge 522, because the lateraldistance AA′, which is equal to AA, is longer than BB. In addition, thedifference in lateral distances AA and BB reduces the possibility that acutting edge region will be subjected to unfavorably high wear forces.

The axis of rotation of the drill head may bifurcate the V-shapedcutting edge of the spade drill into two equal lengths. As shown in FIG.14( a), the drill diameter of the drill head is the lateral distancebetween line N3 tangent to an edge of side insert piece 502 and line N4tangent to an edge of side insert piece 503. The lateral distance fromthe rotational axis 545 of the drill head to line N3 may be the same asthe lateral distance from the rotational axis 545 of the drill head toline N4. Also, the sum of the lengths of the cutting edges 512 b and 522may be the same as the sum of the lengths of the cutting edges 512 a and533.

In certain embodiments, a multi-piece spade drill head for a spade drillaccording to the present disclosure may comprise a center insert pieceforming a central region of the spade drill head, the center insertpiece including first and second sides and a cutting edge. The spadedrill head further comprises a first side insert piece forming at leasta portion of a first side region of the spade drill head, wherein thefirst side insert piece comprises a cutting edge and a mating surfaceconfigured to mate with at least a region of the first side of thecenter insert piece. The spade drill also comprises a second side insertpiece forming at least a portion of a second side region of the spadedrill head, wherein the second side insert piece comprises a cuttingedge and a mating surface configured to mate with at least a region ofthe second side of the center insert piece. The center insert piece, thefirst side insert piece, and the second side insert piece of the spadedrill head are configured to be individually removably secured to a bodyportion with the mating surface of the first side insert piece mated tothe first side of the center insert piece and the mating surface of thesecond side insert piece mated to the second side of the center insertpiece. The insert pieces are mated to align the cutting edge of thecenter insert piece with the cutting edge of each of the first sideinsert piece and the second side insert piece to together form a cuttingedge on an end of the spade drill. The aligned cutting edges of thecenter insert piece and first side insert piece form a first interface,and the aligned cutting edges of the center insert piece and second sideinsert piece form a second interface. A first distance measured from anaxis of rotation of the drill head to the first interface and in adirection perpendicular to the axis of rotation differs from a seconddistance measured from the axis of rotation of the drill head to thesecond interface in a direction perpendicular to the axis of rotation.

According to certain embodiments, a multi-piece spade drill head for aspade drill may comprise a center insert piece comprising a V-shapedcutting edge, and a side insert piece comprising two side regionsseparated by a recess, each side region including a cutting edge. Thecenter insert piece and the side insert piece are configured to beremovably secured to a body portion of the spade drill with the centerinsert piece disposed in the recess of and mating with the side insertpiece, and so that the cutting edge of the center insert piece and thecutting edge of each of the side regions of the side insert piece arealigned to together form a cutting edge on a terminal portion of thespade drill. The aligned cutting edges of the center insert piece andfirst side insert piece form a first interface, and the aligned cuttingedges of the center insert piece and second side insert piece form asecond interface. A first distance measured from an axis of rotation ofthe drill head to the first interface in a direction perpendicular tothe axis of rotation differs from a second distance measured from theaxis of rotation of the drill head to the second interface in adirection perpendicular to the axis of rotation.

FIGS. 15( a)-(c) illustrate one non-limiting embodiment of a multi-piecedrill head according to the present disclosure comprising a centerinsert piece 601 having a generally V-shaped cutting edge 611 includingedges 611 a and 611 b, and two identical side insert pieces 602, 603,each side insert piece comprising a front cutting edge 612, 613 and aside cutting edge 622, 623, respectively. The center insert piece 601 isindexable and can be oriented in a drill head in the cutting orientationshown in FIG. 15( a), or can be rotated 180° about the center of thefasten hole (not numbered) of the center insert piece 601 and orientedin a second cutting orientation, wherein a different cutting edge of thecenter insert piece 601 is presented to the workpiece. The indexablenature of center insert piece 601 is indicated by the indicia “1” and“2” on the depicted face, which identify two possible cuttingorientations between which the center insert piece 601 may be indexed.In one orientation, generally V-shaped cutting edge 611, formed bycutting edge 611 a and cutting edge 611 b, is presented to a workpiece.

As shown in FIG. 15( a) for a top view, side insert pieces 602, 603 aregenerally diamond-shaped and include parallel opposed cutting edges.Side insert piece 602 may comprise a first cutting edge comprising afront cutting edge 612 and a side cutting edge 622, and side insertpiece 603 may comprise a front cutting edge 613 and a side cutting edge623. The length of the first front cutting edge 612 may be differentthan the length of the second front cutting edge 613. The length of theside cutting edges 622, 623 may be the same. Each side insert piece 602,603 is indexable and, in addition to the position shown in FIG. 15( a),may be disposed in a second cutting orientation, in which a differentcutting edge is oriented to contact a workpiece. The short cutting edgeportion 611 b of the center insert piece 601 may be aligned with thelonger cutting edge 612 of the side insert piece 602, and the longercutting edge portion 611 a of the center insert piece 601 may be alignedwith the shorter cutting edge 613 of the side insert piece 603 totogether form a complete cutting edge at an end of the spade drill.

Each of insert pieces 601, 602, and 603 may include one or more chipbreaking features. Center insert piece 601 may include one or more chipbreaking structures 600 on one or more of its cutting edges, such as oncutting edges 611(a) and/or 611(b). At least one of side insert pieces602, 603 may include at least one chip breaking structure 600 on thefront cutting edge. For example, side insert piece 602 may include atleast one chip breaking structure 600 on the front cutting edge 612 andside insert piece 603 may lack chip breaking structures on its frontcutting edge 613. In general, the embodiment of the multi-piece drillhead shown in FIGS. 15( a)-(c), where FIG. 15( a) is a top view, FIG.15( b) a front-end view and 15(c) a bottom view, may be similar to theembodiments shown in FIGS. 13 and 14 with the addition of at least onechip breaker 600 on the cutting edges of the center insert piece 601and/or the front cutting edges of the two side insert pieces 602 and603. The chip breaker may help to break the chips produced during thedrilling process.

According to certain embodiments, a spade drill may comprise anelongated body portion including a shank portion at a first end and asecond end configured to removably receive a drill head, and a removablemulti-piece spade drill head comprising at least three insert pieces.Each insert piece includes a cutting edge and is individually removablysecured to the second end of the body portion adjacent one another andwith the cutting edges of the insert pieces aligned to together form acutting edge on the second end of the body portion of the spade drill.The aligned cutting edges of a first pairing of adjacent insert piecesform a first interface, and the aligned cutting edges of a secondpairing of adjacent insert pieces form a second interface. A firstdistance from an axis of rotation of the drill head to the firstinterface, measured in a direction perpendicular to the axis ofrotation, differs from a second distance from the axis of rotation ofthe drill head to the second interface, measured in a directionperpendicular to the axis of rotation.

According to certain embodiments, the drill head may comprise two insertpieces that mate together to form a generally seamless, generallyV-shaped cutting edge. A two-piece drill head may comprise a centerinsert piece and a single, generally U-shaped side insert piece matedsimultaneously with opposed sides of the center insert piece. The centerinsert piece may comprise a longer cutting edge portion and a shortercutting edge portion. The side insert piece may comprise a longer frontcutting edge and a shorter front cutting edge. The longer cutting edgeportion of the center insert piece may be aligned with the shorter frontcutting edge of the side insert piece to form a first interface. Theshorter cutting edge portion of the center insert piece may be alignedwith the longer front cutting edge of the side insert piece to form asecond interface. The lateral distance measured in a directionperpendicular to a rotational axis of the drill head from the rotationalaxis to the first interface may differ from the lateral distance fromthe rotational axis of the drill head to the second interface.

In certain embodiments, a spade drill may comprise an elongated bodyportion including a shank portion at a first end and a second endconfigured to removably receive a drill head, and a removablemulti-piece spade drill head comprising a center insert piece forming acentral region of the spade drill head. The center insert piece includesfirst and second sides and a cutting edge. A first side insert pieceforms at least a portion of a first side region of the spade drill head,and the first side insert piece comprises a cutting edge and a matingsurface configured to mate with at least a region of the first side ofthe center insert piece. A second side insert piece forms at least aportion of a second side region of the spade drill head, and the secondside insert piece comprises a cutting edge and a mating surfaceconfigured to mate with at least a region of the second side of thecenter insert piece. The center insert piece, the first side insertpiece, and the second side insert piece are configured to beindividually removably secured to the body portion, with the matingsurface of the first side insert piece mated to the first side of thecenter insert piece, and the mating surface of the second side insertpiece mated to the second side of the center insert piece. In this way,the cutting edge of the center insert piece is aligned with the cuttingedge of each of the first side insert piece and the second side insertpiece to together form a cutting edge on an end of the spade drill. Thealigned cutting edges of the center insert piece and first side insertpiece form a first interface, and the aligned cutting edges of thecenter insert piece and second side insert piece form a secondinterface. A first distance measured in a direction perpendicular to anaxis of rotation of the drill head from the axis of rotation to thefirst interface differs from a second distance measured in a directionperpendicular to the axis of rotation of the drill head from the axis ofrotation to the second interface.

In other embodiments, a spade drill may comprise an elongated bodyportion including a shank portion at a first end and a second endconfigured to removably receive a drill head, and a removablemulti-piece spade drill head. The drill head comprises a center insertpiece comprising a V-shaped cutting edge, and a side insert piececomprising two side regions separated by a recess, each side regionincluding a cutting edge. The center insert piece and the side insertpiece are configured to be removably secured to the body portion of thespade drill with the center insert piece disposed in the recess of andmating with the side insert piece and so that the V-shaped cutting edgeof the center insert piece and the cutting edge of each of the sideregions of the center insert piece are aligned to together form acutting edge on the second end of the spade drill. The aligned cuttingedges of the center insert piece and one of the two side regions of theside insert piece form a first interface, and the aligned cutting edgesof the center insert piece and the other of the two side regions of theside insert piece second side insert piece form a second interface. Afirst distance measured in a direction perpendicular to an axis ofrotation of the drill head from the axis of rotation to the firstinterface differs from a second distance measured in a directionperpendicular to the axis of rotation of the drill head from the axis ofrotation to the second interface.

Although the above embodiments each include two or three separate insertpieces, it will be evident from the present description that drill headsconstructed according to the present disclosure may include more thanthree individually removable insert pieces. For example, to providefurther enhanced cutting edge wear resistance as a distance from therotational axis of the drill head increases, multi-piece drill headsaccording to the present disclosure may include, for example, a centerinsert piece and 3 to 7, or more, side insert pieces. In a possibleembodiment of a five-piece drill head embodiment according to thepresent disclosure, for example, the drill head may include: a centerinsert piece secured to a holder; a pair of first side insert pieces,one such first side insert piece mated against each of the two sides ofthe center insert piece and separately secured to the tool holder (or,alternatively, a single side insert piece having a generally U-shapedconstruction similar to that in FIGS. 11( a)-(b)); and a pair of secondside insert pieces, one such second side insert piece mated against anoutwardly exposed side of each first side insert piece and separatelysecured to the tool holder. As such, a distance between the outerexposed edges of the two second insert pieces defines the cuttingdiameter of the drill head. The second insert pieces may be made ofcemented carbide or another material having greater wear resistance thanthe first side insert pieces. The first insert pieces (or piece), inturn, are made of cemented carbide or another material having greaterwear resistance than the center insert piece. In this way, the increasedcutting speed and consequent increased propensity for wear at positionsdistant from the rotational axis of the drill head are counteracted bythe progressively enhanced wear resistance properties of the first andsecond insert pieces. The center insert piece, first side insert pieces(or piece), and second insert pieces may be separately replaced and/ormay be designed so as to be indexable between two or more cuttingorientations to present a new cutting edge to the workpiece when wearand/or damage to the cutting edge becomes unacceptable.

Accordingly, embodiments of multi-piece drill heads and drills of anovel design according to the present disclosure may be designed with awide range of geometric features that a conventional one-piece soliddrill or indexable drill insert may posses. Embodiments of multi-piecedrill heads according to the present disclosure may be, for example, ofconventional size and adapted for conventional use in a variety ofdrilling applications.

It will be understood that the present description illustrates thoseaspects of the invention relevant to a clear understanding of theinvention. Certain aspects that would be apparent to those of ordinaryskill in the art and that, therefore, would not facilitate a betterunderstanding of the invention, have not been presented in order tosimplify the present description. For example, it will be understoodthat the insert pieces and other components making up multi-piece drillheads and drills according to the present disclosure may be made fromconventional materials using conventional manufacturing techniques knownto those having ordinary skill in the art. As such, possiblemanufacturing techniques will be readily known to those of ordinaryskill upon considering the present description and are not describedherein.

Also, although only a limited number of embodiments of multi-piece drillheads according to the present description necessarily are describedherein, one of ordinary skill in the art will, upon considering theforegoing description, recognize that many modifications and variationsof the invention may be employed. All such variations and modificationsof the invention are intended to be covered by the foregoing descriptionand the following claims. The foregoing examples of possible designs formulti-piece drill heads and drilling assemblies according to the presentdisclosure are offered by way of example only, and are not exhaustive ofall designs within the scope of the present disclosure. Those havingordinary skill, upon reading the present disclosure, may readilyidentify additional designs that are embodiments within the scope of thepresent disclosure. It is understood, therefore, that this invention isnot limited to the particular embodiments disclosed herein, but it isintended to cover modifications that are within the principle and scopeof the invention, as defined by the claims.

1. A multi-piece spade drill head for a spade drill, the spade drillcomprising an elongate body portion and a cutting portion removablysecured to an end of the body portion, the multi-piece spade drill headcomprising: at least three insert pieces, each piece including a cuttingedge, wherein the at least three insert pieces are configured to beremovably secured to the body portion adjacent one another with thecutting edges aligned to together form a cutting edge on an end of thespade drill; wherein the aligned cutting edges of adjacent insert piecesform a first interface and a second interface; and wherein a firstdistance measured in a direction perpendicular to an axis of rotation ofthe drill head from the axis of rotation to the first interface differsfrom a second distance measured in a direction perpendicular to the axisof rotation from the axis of rotation to the second interface.
 2. Themulti-piece spade drill head of claim 1, wherein at least one of thethree insert pieces includes two cutting edges and is configured to beindividually indexable and secured to the body portion in two cuttingorientations, wherein in each cutting orientation a different cuttingedge is aligned with cutting edges of the remaining insert pieces toform the cutting edge on the end of the spade drill when the inserts areremovably secured to the body portion of the spade drill.
 3. Themulti-piece spade drill head of claim 1 comprising a center insert pieceand two side insert pieces, wherein the two side insert pieces areconfigured to be removably secured to the body portion mated withopposed sides of the center insert piece.
 4. The multi-piece spade drillhead of claim 3, wherein each side insert piece includes a matingsurface configured to mate with a complementarily shaped region of aside of the center insert piece when the center insert piece and sideinsert pieces are removably secured to the body portion of the spadedrill.
 5. The multi-piece spade drill head of claim 4, wherein at leastone of the three insert pieces includes two cutting edges and isconfigured to be individually indexable and secured to the body portionin two cutting orientations, wherein in each cutting orientation adifferent cutting edge is aligned with cutting edges of the remaininginsert pieces to form the cutting edge on the end of the spade drillwhen the inserts are removably secured to the body portion of the spadedrill.
 6. The multi-piece spade drill head of claim 3, wherein thecenter insert piece comprises a longer cutting edge portion and ashorter cutting edge portion, and each of the two side insert piecescomprise a longer cutting edge portion and a shorter cutting edgeportion, and wherein the two side insert pieces are configured to beremovably secured to the body portion mated with opposed sides of thecenter insert piece.
 7. The multi-piece spade drill head of claim 6,wherein each side insert piece includes a mating surface configured tomate with a complementarily shaped region of a side of the center insertpiece when the center insert piece and side insert pieces are removablysecured to the body portion of the spade drill, wherein the longercutting edge portion of the center insert piece is mated with theshorter cutting edge portion of one of the two side insert pieces andthe shorter cutting edge portion of the center insert piece is matedwith the longer cutting edge portion of the other of the two side insertpieces.
 8. The multi-piece spade drill head of claim 7, wherein thefirst distance measured in a direction perpendicular to the axis ofrotation from the axis of rotation to the first interface between thelonger cutting edge portion of the center insert piece and the shortercutting edge portion of one of the two side insert pieces differs fromthe second distance measured in a direction perpendicular to the axis ofrotation from the axis of rotation to the second interface comprisingthe shorter cutting edge portion of the center insert piece and thelonger cutting edge portion of the other of the two side insert pieces.9. The multi-piece spade drill head of claim 8, wherein the axis ofrotation of the drill head bifurcates the cutting edge on an end of thespade drill into two equal lengths.
 10. The multi-piece spade drill headof claim 1, wherein each of the insert pieces is made of materialindividually selected from a cemented carbide material and a hard steel.11. The multi-piece spade drill head of claim 3, wherein each of thethree insert pieces is made of material individually selected from acemented carbide material and a hard steel.
 12. The multi-piece spadedrill head of claim 10, wherein at least two of the insert pieces aremade of different materials.
 13. The multi-piece spade drill head ofclaim 12, wherein at least two of the insert pieces are made ofdifferent materials.
 14. The multi-piece spade drill head of claim 1comprising a center insert piece made of a first material and two sideinsert pieces made of a second material, wherein the two side insertpieces are configured to be removably secured to the body portion of thespade drill mated with opposed sides of the center insert piece, andwherein the second material has greater wear resistance than the firstmaterial.
 15. The multi-piece spade drill head of claim 14, wherein atleast one of the center insert piece and the side insert pieces includestwo cutting edges and is configured to be individually indexable andsecured to the body portion in two cutting orientations, wherein in eachcutting orientation a different cutting edge is aligned with cuttingedges of the remaining insert pieces to form the cutting edge on the endof the spade drill when the inserts are removably secured to the bodyportion of the spade drill.
 16. The multi-piece spade drill head ofclaim 1, wherein each of the center insert piece and the side insertpieces is made of material individually selected from a cemented carbidematerial and a hard steel.
 17. A multi-piece spade drill head for aspade drill, the spade drill comprising a body portion and a drill headremovably secured to the body portion, the multi-piece spade drill headcomprising: a center insert piece forming a central region of the spadedrill head, the center insert piece including first and second sides anda cutting edge; a first side insert piece forming at least a portion ofa first side region of the spade drill head, the first side insert piececomprising a cutting edge and a mating surface configured to mate withat least a region of the first side of the center insert piece; and asecond side insert piece forming at least a portion of a second sideregion of the spade drill head, the second side insert piece comprisinga cutting edge and a mating surface configured to mate with at least aregion of the second side of the center insert piece; wherein the centerinsert piece, the first side insert piece, and the second side insertpiece are configured to be individually removably secured to the bodyportion with the mating surface of the first side insert piece mated tothe first side of the center insert piece and the mating surface of thesecond side insert piece mated to the second side of the center insertpiece to thereby align the cutting edge of the center insert piece withthe cutting edge of each of the first side insert piece and the secondside insert piece to together form a cutting edge on an end of the spadedrill; and wherein the aligned cutting edges of the center insert pieceand first side insert piece form a first interface, and the alignedcutting edges of the center insert piece and second side insert pieceform a second interface; and wherein a first distance measured in adirection perpendicular to an axis of rotation of the drill head fromthe axis of rotation to the first interface differs from a seconddistance measured in a direction perpendicular to the axis of rotationfrom the axis of rotation to the second interface.
 18. The multi-piecespade drill head of claim 17, wherein at least one of the center insertpiece, the first side insert piece, and the second side insert piececomprises two cutting edges and is configured to be individuallyindexable and secured to the body portion in two cutting orientations,wherein in each cutting orientation a different cutting edge is alignedwith cutting edges of the remaining at least one of the center insertpiece, the first side insert piece, and the second side insert piece toform the cutting edge on the end of the spade drill when the inserts areremovably secured to the body portion of the spade drill.
 19. Themulti-piece spade drill head of claim 17, wherein the mating surface ofthe first side insert piece and mating surface of the second side insertpiece each mate with a complementary-shaped region of the center insertpiece
 20. The multi-piece spade drill head of claim 17, wherein each ofthe center insert piece, the first side insert piece, and the secondinsert piece is individually made of a material selected from a cementedcarbide material and a hard steel.
 21. The multi-piece spade drill headof claim 20, wherein at least two inserts selected from the centerinsert piece, the first side insert piece, and the second insert pieceare made of different materials.
 22. The multi-piece spade drill head ofclaim 21, wherein the center insert piece is made of a first materialand the first side insert piece and the second side insert piece aremade of a second material, and wherein the second material has greaterwear resistance than the first material.
 23. The multi-piece spade drillhead of claim 17, wherein the center insert piece is made of a firstmaterial and the first side insert piece and the second side insertpiece are made of a second material, and wherein the second material hasgreater wear resistance than the first material.
 24. A spade drillcomprising: an elongated body portion including a shank portion at afirst end and a second end configured to removably receive a drill head;and a removable multi-piece spade drill head comprising at least threeinsert pieces, each insert piece including a cutting edge andindividually removably secured to the second end of the body portionadjacent one another and with the cutting edges of the insert piecesaligned to together form a cutting edge on the second end of the bodyportion of the spade drill; wherein the aligned cutting edges of theadjacent insert pieces form a first interface and the aligned cuttingedges of the other adjacent insert pieces form a second interface; andwherein a first distance measured in a direction perpendicular to anaxis of rotation of the drill head from the axis of rotation to thefirst interface differs from a second distance measured in a directionperpendicular to the axis of rotation from the axis of rotation to thesecond interface.
 25. The spade drill of claim 24, wherein at least oneof the three insert pieces includes two cutting edges and is configuredto be individually indexable and secured to the body portion in twocutting orientations, wherein in each cutting orientation a differentcutting edge is aligned with cutting edges of the remaining insertpieces to form the cutting edge on the second end of the spade drillwhen the insert pieces are removably secured to the body portion of thespade drill.
 26. The spade drill of claim 24, wherein the multi-piecespade drill head comprises a center insert piece and two side insertpieces, wherein the two side insert pieces are removably secured to thebody portion mated with opposed sides of the center insert piece. 27.The spade drill of claim 26, wherein each side insert piece includes amating surface mated with a complementarily shaped region of a side ofthe center insert piece.
 28. The spade drill of claim 27, wherein atleast one of the center insert piece and the two side insert pieces ofthe drill head is configured to be individually indexable and secured tothe body portion in two cutting orientations, wherein in each cuttingorientation a different cutting edge is aligned with cutting edges ofthe remaining insert pieces to form the cutting edge when the insertpieces are removably secured to the second end of the body portion. 29.The spade drill of claim 26, wherein each of the center insert piece andthe two side insert pieces of the spade drill head is made of a materialindividually selected from a cemented carbide material and a hard steel.30. The spade drill of claim 26, wherein at least two of the centerinsert piece and the two side insert pieces of the spade drill head aremade of different materials.
 31. The spade drill of claim 30, whereinthe center insert piece is made of a first material and the side insertpieces are made of a second material, and wherein the second materialhas greater wear resistance than the first material.
 32. A spade drillcomprising: an elongated body portion including a shank portion at afirst end and a second end configured to removably receive a drill head,and a removable multi-piece spade drill head comprising: a center insertpiece forming a central region of the spade drill head, the centerinsert piece including first and second sides and a cutting edge; afirst side insert piece forming at least a portion of a first sideregion of the spade drill head, the first side insert piece comprising acutting edge and a mating surface configured to mate with at least aregion of the first side of the center insert piece; and a second sideinsert piece forming at least a portion of a second side region of thespade drill head, the second side insert piece comprising a cutting edgeand a mating surface configured to mate with at least a region of thesecond side of the center insert piece; wherein the center insert piece,the first side insert piece, and the second side insert piece areconfigured to be individually removably secured to the body portion withthe mating surface of the first side insert piece mated to the firstside of the center insert piece and the mating surface of the secondside insert piece mated to the second side of the center insert piece toalign the cutting edge of the center insert piece with the cutting edgeof each of the first side insert piece and the second side insert pieceto together form a cutting edge on an end of the spade drill; whereinthe aligned cutting edges of the center insert piece and first sideinsert piece form a first interface and the aligned cutting edges of thecenter insert piece and second side insert piece form a secondinterface; and wherein a first distance measured in a directionperpendicular to an axis of rotation from the axis of rotation to thefirst interface differs from a second distance measured in a directionperpendicular to the axis of rotation from the axis of rotation to thesecond interface.
 33. The spade drill of claim 32, wherein at least oneof the center insert piece, the first side insert piece, and the secondside insert piece comprises two cutting edges and is individuallyindexable and configured to be removably secured to the second end bodyportion in two cutting orientations, wherein in each cutting orientationa different cutting edge is aligned with cutting edges of the remainingat least one of the center insert piece, the first side insert piece,and the second side insert piece to form the cutting edge on the secondend of the body portion of the spade drill.
 34. The spade drill of claim32, wherein the mating surface of the first side insert piece and matingsurface of the second side insert each mate with a complementary-shapedregion of the center insert piece.
 35. The spade drill of claim 33,wherein each of the center insert piece, the first side insert piece,and second side insert piece of the spade drill head is individuallymade of a material selected from a cemented carbide material and a hardsteel.
 36. The spade drill of claim 35, wherein at least two of thecenter insert piece, the first side insert piece, and second side insertpiece of the spade drill head are made of different materials.
 37. Thespade drill of claim 36, wherein the center insert piece is made of afirst material and the first side insert piece and second side insertpiece are made of a second material, and wherein the second material hasgreater wear resistance than the first material.
 38. A multi-piece spadedrill head for a spade drill, the spade drill comprising an elongatebody portion and a cutting portion removably secured to an end of thebody portion, the multi-piece spade drill head comprising: a centerinsert piece comprising a V-shaped cutting edge; and a side insert piececomprising two side regions separated by a recess, each side regionincluding a cutting edge; wherein the center insert piece and the sideinsert piece are configured to be removably secured to the body portionof the spade drill with the center insert piece disposed in the recessof and mating with the side insert piece and so that the cutting edge ofthe center insert piece and the cutting edge of each of the side regionsof the side insert piece are aligned to together form a cutting edge ona terminal portion of the spade drill; wherein the aligned cutting edgesof the center insert piece and first side insert piece form a firstinterface and the aligned cutting edges of the center insert piece andsecond side insert piece form a second interface; and wherein a firstdistance measured in a direction perpendicular to an axis of rotation ofthe drill head from the axis of rotation to the first interface differsfrom a second distance measured in a direction perpendicular to the axisof rotation from the axis of rotation to the second interface.
 39. Themulti-piece spade drill head of claim 38, wherein the center insertpiece includes a plurality of cutting edges and is configured to beindividually indexable and secured to the body portion in two cuttingorientations, wherein in each cutting orientation a different V-shapedcutting edge of the center insert piece is aligned with cutting edges ofthe side regions of the side insert piece to form the cutting edge onthe terminal portion of the spade drill when the inserts are removablysecured to the body portion of the spade drill.
 40. The multi-piecespade drill head of claim 38, wherein each side region of the sideinsert piece includes a mating surface configured to mate with acomplementarily shaped region of a side of the center insert piece whenthe center insert piece and side insert piece are removably secured tothe body portion of the spade drill with the center insert piecedisposed in the recess of the side insert piece.
 41. The multi-piecespade drill head of claim 38, wherein the center insert piece and theside insert piece are made of a material individually selected from acemented carbide material and a hard steel.
 42. The multi-piece spadedrill head of claim 41, wherein the center insert piece and the sideinsert piece are made of different materials.
 43. The multi-piece spadedrill head of claim 42, wherein the center insert piece is made of afirst material, the side insert piece is made of a second material, andthe second material has greater wear resistance than the first material.44. A spade drill comprising an elongated body portion including a shankportion at a first end and a second end configured to removably receivea drill head, and a removable multi-piece spade drill head comprising: acenter insert piece comprising a V-shaped cutting edge; and a sideinsert piece comprising two side regions separated by a recess, eachside region including a cutting edge; wherein the center insert pieceand the side insert piece are configured to be removably secured to thebody portion of the spade drill with the center insert piece disposed inthe recess of and mating with the side insert piece and so that theV-shaped cutting edge of the center insert piece and the cutting edge ofeach of the side regions of the center insert piece are aligned totogether form a cutting edge on the second end of the spade drill;wherein the aligned cutting edges of the center insert piece and one ofthe two side regions of the side insert piece form a first interface andthe aligned cutting edges of the center insert piece and the other ofthe two side regions of the side insert piece second side insert pieceform a second interface; and wherein a first distance measured in adirection perpendicular to an axis of rotation of the drill head fromthe axis of rotation to the first interface differs from a seconddistance measured in a direction perpendicular to the axis of rotationfrom the axis of rotation to the second interface.
 45. The spade drillof claim 44, wherein the center insert piece includes a plurality ofcutting edges and is configured to be individually indexable and securedto the body portion in two cutting orientations, wherein in each cuttingorientation a different V-shaped cutting edge of the center insert pieceis aligned with cutting edges of the side regions of the side insertpiece to form the cutting edge on the second end of the spade drill whenthe inserts are removably secured to the body portion of the spadedrill.
 46. The spade drill of claim 44, wherein each side region of theside insert piece includes a mating surface configured to mate with acomplementarily shaped region of a side of the center insert piece whenthe center insert piece and side insert piece are removably secured tothe body portion of the spade drill with the center insert piecedisposed in the recess of the side insert piece.
 47. The spade drill ofclaim 44, wherein the center insert piece and the side insert piece aremade of a material individually selected from a cemented carbidematerial and a hard steel.
 48. The spade drill of claim 47, wherein thecenter insert piece and the side insert piece are made of differentmaterials.
 49. The spade drill of claim 48, wherein the center insertpiece is made of a first material, the side insert piece is made of asecond material, and the second material has greater wear resistancethan the first material.